Fix MBR Slave Drive

fixmbr only works on the startup disk.  Check out the "fixing mbr's..." section

http://technet.microsoft.com/en-us/library/bb457122.aspx#EEAA

Try disabling the root disk in bios, change boot order to boot from the suspect drive then do the repair.

Followup Info:  I've just noticed when I plug in the USB hard drive I get a message statiing the device exceeds power limits for this port.  I've already researched this error to determine I might need an external power supply.  But, would this error keep the drive from being recognized?

Hook the bad drive back to laptop and use XP CD to run repair from there. If you hook the drive on desktop, then you will face other issue with different HAL.

What happens if you do fresh installation when the drive in laptop? are you having data on the bad drive to try recovery?

"But, would this error keep the drive from being recognized?"

Most definitely YES

i suggest to ALWAYS use  USB devices with their own power source, as you can easily overload  an usb port, and ruin it.
for your problem : what happened with the laptop?
maybe running a chkdsk on the disk, or a repair install can cure it.
chkdsk :  http://support.microsoft.com/kb/314058
repair install : http://www.michaelstevenstech.com/XPrepairinstall.htm      

To Punky:  There is data on the hard drive that I need to recover; so, I don't want to try a fresh install.

To nobus:  I'm picking up an external power supply today 01/28.  Will try your links' solutions then.

thanks - but what happened to the laptop ?

Original laptop (with suspect hard drive) is an HP.  That's the laptop from which I have removed hard drive.  I now have that hard drive connected via USB to a Toshiba laptop.  It is the Toshiba that does NOT recognize the suspected defective hard drive that came out of the HP.

again - what was the problem ? any messages ?

Once the (working) Toshiba boots up to the desktop, entering "My Computer" reveals the C:drive and CDROM drive.  The hard drive that was removed from the HP is now encased in an adapter that allows it to connect to a USB port.  When I plug that hard drive into the USB port of the "working" Toshiba, an error appears stating "the device exceeds power limits" for this port - and, the hard drive does not show up under "My Computer."

Thanks, nobus.  Picked up a power supply from Radio Shack, connected hard drive to the "working" Toshiba, everything shows up as expected under "My Computer", and have already retrieved needed data.

good to hear !