New system build, old HD, do I need to reformat

if its XP then it propably wont boot without a repair install

How to Perform a Windows XP Repair Install
http://michaelstevenstech.com/XPrepairinstall.htm

How to Perform an In-Place Upgrade (Reinstallation) of Windows XP
http://support.microsoft.com/default.aspx?scid=kb;en-us;315341

but Ive seen systems still fail even after this is done, you said you had DRIVED hinting more than one? if so you can flattem one (clean install) and install the second one. and windows will see it - you need to make a judgement call on weather you need to save any data off the drive(s) first.

if you decide to flatten it and rebuild (I would) then just fit one drive and do a fresh install

Perform a clean install of Windows XP (Erase Everything!!)


Before you start

1.Make sure your data is backed up, don’t forget things like your favourites folder, my documents etc
2.Make sure you have the unlock code for Windows XP
3.Make sure you have the relevant drivers for you hardware and they are compatible with Windows XP

  a.To find out if your hardware is compatible go here http://www.microsoft.com/whdc/hcl/default.mspx
  b.To find out what hardware you have, to get the correct drivers go here http://www.lavalys.com/products/download.php?dlid=1&lang=en

Note: At the very minimum have your Modem drivers then you can download any drivers you ‘thought you had.’

**********


1.Set your PC’s boot order to boot from CD BEFORE your hard drive (usually IDE0)
2.Place the CD in the drive and reboot.
3.At the ‘Press any key to boot from CD…’ press a key
4.If your PC WONT boot from CD boot from a win98 floppy disk, try www.bootdisk.com and enable CD support then type “cd D:\i386\setup (or winnt) If D:\is your CD drive letter it may not be, check! Your boot order MUST be set so that the floppy is checked before the hard drive for this to work, also ensure when the boot disk is loading you see RAMDRIVE start up or it will run like a two legged dog!
5.At the welcome screen press enter (you can press R here to repair an existing installation)
6.At the license agreement press F8
7.Hard Drive partitioning

  a.If it’s a shiny new drive it will find it un-partitioned if you want one big C: drive just press Enter (then go to step 8)
  b.If it finds an old partition you can delete by pressing D then you get a warning, Press ENTER, Press L to confirm. (then see a) above.
  c.If you want to create more than one partition (i.e. have hard Drive C:\ and D:\ etc). Ensure the ‘un-partitioned space is highlighted and press C. type in the amount of space you want to use (in Megabytes) for the Partition – there will always be a small amount you cant partition don’t worry! Then Press Enter to continue, you can keep doing this until all the space is used up. When finished select the partition you want to put XP on and press enter.

8.You will now be asked to format the partition, unless you have Win98 also installed or need to get to the drive from another operating system (i.e. on the same machine, NOT over a network) then select NTFS formatting if you do need to do any of the above choose FAT32 formatting.
9.Go and put the kettle on, this will take a while!
10.When its done it will copy a lot of files over to the hard drive, time to fit in more coffee!
11.The system will then reboot (after a 15 second countdown – to force it to do it now press enter)
12.Your now in the Nice looking stage of the setup, you will see the black XP loading screen.
13.For a long time the install will do its own thing check its progress on the left hand side.
14.You will be asked to enter your language and input locales, do so, and get the input locales right or all your symbols will be on the wrong keys! Press Next.
15.You will need to enter you name and Organisation info when done Press Next.
16.Aha! Pirates beware, time to enter the unlock code, if you have a typo you can go back and correct it (don’t panic) Press Next.
17.Pick a sensible name for the PC (the default one is not usually intuitive) and enter an administrator’s password (twice) DO NOT EVER FORGET THIS PASSWORD.
18.Time to tell the PC where you are, check the time zone, which annoyingly are always set to Tijuana (unless you live in Tijuana of course!) if your in the UK don’t forget to tick the daylight saving time box. Click Next
19.The next input will be Network settings you can always configure these later at your leisure so I usually click Next here, If you want to configure your IP address etc, select custom settings before clicking next and follow the onscreen prompts.
20.Phew! Time for another coffee you’ve got another wait on your hands.
21.After its finished it will reboot and USUALLY tell you its going to resize you monitor resolution just click OK and let it go, if it all goes to pot here DO NOTHING it will revert back!
22.Depending on your version it will now either

  a.Log into windows fine
  b.Present you with the administrators logon prompt
  c.Launch a welcome to windows session to configure more users and connect to Microsoft to register (you can skip the registration bit if you like)

23.After all that you will be looking at a fresh install of windows, now its time to put all the latest drivers back in and restore your data.

*****Links*****
http://alpha.fdu.edu/csci/Windows_2000.pdf
http://www.blackviper.com/Articles/OS/OSguides.htm (Excellent!)

How To install Windows XP (Includes Upgrade Path)
http://support.microsoft.com/default.aspx?scid=kb;EN-US;316941

Clean installing Windows XP
http://www.webtree.ca/windowsxp/clean_install.htm

A Guide to Installing Windows XP
http://www.pro-networks.org/XPMaNiA/install.shtml

Along with what was already said above.  Here is a website that is a tell-all about pc hardware.  It has a bunch of How-To's along with a complete guide on building a pc

PeteLong - Thank you so much for that detailed answer.  I am sure it took a fair amount of time and effort to put it together and I would love to reward it, however, my question was best answered by coral47.  My real question was whether I could test the MOBO before I installed the drives and what the first steps would be.  I didn't know if I had to reformat before testing the motherboard or after.  I was already planning to wipe the drives and perform a clean install, I just didn't know if I had to do that before testing the board.  Thank you all for your help.

Thank you much.    : )

Note: If it does not boot up outside the case, it does not mean it is a bad mobo. There are several reasons for it not to. It's just easier to test it this way.