That's true, but it isn't going to do him any good if the old processor won't fit on the new motherboard because it is a different form factor. I am talking about the computer processor, not the video card prcessor. If the card is a PCI E, then use a PCI E motherboard. Same with AGP. But I'm more concerned because he wants to replace thre motherboard so he can use a PCI E card, but he didn't mention anything about the processor. Oh, and also, you might have to upgrade your power supply too. LOL. I know this sounds like a lot, but it's not.
Do you have a make and model number for your computer? You can go on the web site and go to tech support and see what kind of processor your computer is using. Or you can post it on here and I will look for you. Like I say, you just want to make sure your old processor will work with your new motherboard, or you are going to have to replace the processor too.