1)Since you are changing chipsets, it is recommend that you reinstall the Operating System.
2)This motherboard supports both AGP and PCIe: http://www.asrock.com/product/775Dual-VSTA.htm
You might want to make the jump to the newer video card format, as well as all the other new items format. You will get better performance.
Make a backup of your old HD and get yourself a new one. This thing won't boot with a setup that different. And you're running win 98 or something I guess? allthemore a reason to get a new disc and not even try using the old one. 100:1 that it doesn't work...
Just suggest an el cheapo eMachine or Dell.. and I mean el cheapo.. like the $250 variety. The bonus here is the inclusion of an OS. Every part gets an upgrade. It's much more cost-effective, she gets free tech support (ie. not you), free warranty, and parts are guaranteed compatible. Hook up old drive as a slave and copy over her pics, e-mails, bookmarks, etc. to the new drive.
Come on, do you really want to deal with that dusty old machine? You will have to reformat and reinstall the OS. Between the chipset, RAM, and processor, Win98 (I'm guessing?) won't know what hit it.
you can do it but the amount of trouble and work
is horrendous ,, need os install disk and every driver
(chipset,video etc) to get it to work maybe
have done it a couple of times but not really worth it
go with fluff or qwertycopter suggestion
makes life much easier