PCI and PCI express are 2 different slot types. I'm assuming the card you have is a PCI... maybe an AGP, but from what I have tried to look up it's PCI only. your best solution in all honesty, is to save up and build/buy a whole new system. to be totally sure about the card though. try this:
http://www.belarc.com/free_download.html
this will give you an HTML profile of your system and tell you what you need to know. but before posting X out all personal info (CD keys near the bottom, etc..)
but I still think you should hold off and get a whole new system