|Don't confuse PCI with PCI-express. PCI sucks. Your board has AGP so why would you wanna downgrade to PCI?|
I think there's something missing from your story...like why did you feel you had to use the restore discs? That tells me that you were having major problems. You can't fix a hardware problem by reinstalling the operating system & it would appear that your problem is hardware related.
BTW, since PCI-e has taken over as the primary video card format, decent AGP cards have become very expensive. Then again, the FX5700LE is pretty crappy so just about anything would be an improvement. 512MB doesn't make a card any faster & isn't absolutely necessary but it's pretty hard to avoid these days.
Here's a cheap open box Radeon X1650 Pro. It uses slow GDDR2 memory though. Cards with faster GDDR3 run closer to $100. Note the 4-pin aux power requirement: