if you're not willing to reinstall xp on your computer, how about a virtual machine instead?
it's pretty straight forward, and it'll give you a clean enviroment to fart around in, without messing with your computer that you can't touch. you'll need admin rights on the computer to make it install correctly, but after that regular rights are ok.
1) goto
www.vmware.com and download + install VMWare Player
2) goto
www.easyvmx.com and use the super easy wizard to create an empty virtual machine for you.
3) after downloading and unzipping the file from easyvmx, put your windows xp (or 2000 or 98) cd in your cd drive, and double click the .vmx file
4) VMWare Player will open up, and proceed to boot from your windows cd. follow the instructions for installing windows.
5) Now you'll have a clean copy of windows, running in a window. Download mplab from microchip, and see what happens.
You're not going to be able to use a low level programmer from inside your virtual machine, since they are timing critical. however, a high level programmer like the ICD2 or anything USB will work. However, this exercise will help you get mplab running. If it works, then you know your windows is hosed, and needs to be reinstalled.
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couple of side notes:
www.easyvmx.com appears to be down at the time this was written, hopefully it will be back up soon
installing a 'virtual' copy of windows on a computer already running windows is not permitted by the All Powerful Microsoft, so you run the risk of having the Thought Police bust down your door and haul you off to some godless island should you decide to install it.
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edit: it seems easyvmx may have been shut down, so as not to provide outdated information, here's a site with links to other sources for building vmx files:
**broken link removed**