Best/Easiest way to get remote access to PC I have LAN access to...

The easiest SW for remote access in terms of explaining to non-IT people is TeamViewer (www.teamviewer.com).

Sorry - I should have been more clear.  This is for business use and I'm looking for something free.... (or has some nominal cost)... TV is hundreds of dollars for business use.

Thanks!

team viewer quick support is free, you need one licence for team viewer full install (to connect out to other machines) and have team viewer quick support running on clients

dameware has an auto install/run feature too, but it's not free though.

But AFAIK you should be able to use VNC without installation, just by starting a batch file - which is ok for internal use.

Do you have LAN access to the remote machines?

Yes - I have access to PC's on the same LAN.  I'd like something ridiculously simple to tell someone...
like
"Go here \\192.168.1.x\share and then double click xyz"  No install... no password setup... just tells them their own IP so I can then use my vnc viewer of choice to remote into their PC"

How many VNC users are we talking?  

not many.  Almost all the PCs at our company have logmein installed.  However somehow it never fails that somebody has some problem in some PC that does not have it.... Then somehow I wind up wasting half an hour just trying to get into their PC and do stuff... I want a way that I can reliably get into a PC remotely in seconds/minutes... I have somebody standing in front of the remote PC on the phone... And I have access to the same local network...

I second serial band's solution for RDP. just enable it through the remote registry entry as he said. you can then connect by internal IP

RDP doesn't produce an interactive session, so a user cannot reproduce a problem whilst you see how they do it.  VNC is the better option.

If it's not many computers, then create a spreadsheet of the computer names / user names and when they ring you, connect using VNC via computer name or, whilst they're describing the problem, ping their computer name to get the IP?

RDP does allow interactive sessions but the user has to request assistance ... the helper then gets a message saying that help is needed ... when they click to agree to give help, both users can see the screen ... that is an interactive session. total cost = no charge

Remote Assistance does create such an interactive session, but I cannot remember how far you can automate it to allow for easy use.

From the Expert answers up to now I have to derive that installation is required for VNC? I think not. Just having the server process started on demand (via batch file) should be fine.  E.g. RealVNC:

@echo off
set /p .=Please tell the support staff your computer name: <nul & hostname
\\server\share\PathToVNC\winvnc4.exe -showstatus=0

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to automate remote assistance you would save the remote assistance invite file which is generated by the assistance request and save it to desktop.

users can then double click the desktop file to invoke the "assist me" request

your batch file should work fine but I could just point out that instead of running ultravnc.exe you could also  call the quick support ,"teamviewer_QS_en.exe "or even set to boot at start up. as I said earlier you o  see liars of ways lolnly need one 1 team viewer licence for the full version which would be machine you are connecting from, all the other  PCs would run the standalone Team viewer quick support executable. the 9 digit partner ID is unique to each machine so it doesn't change. users would need to read our the 4 digit pass word code  ...

Nice call Jambon, I wasn't aware the remote assistance invite files could be saved :)