Yes, I'd upgrade to 2GB RAM and buy the card but that's maybe all you'll be able to add to your system. If it doesn't work then just return it but keep the RAM.
Two items I'll mention before I go. 1) These cards run hot (60C+) so you might notice some heat problems after installing it. The symptoms are erratic computer performance and hangs usually of a monetary nature not permanent crashes. (An Event that require a restart of the system.) Use compressed air to clean out the inside of the tower on a regular basis and especially, thoroughly clean the CPU cooler. You should already be doing this and if you aren't then learn how, it's simple to do. All computers need a good cleaning once in awhile, with a graphics cards or not. 2) If possible disable any chip set graphic you might have to conserve power. You can find out if you have a chip set by opening device manager. This is how you get there: start>control panel>administrative tools>computer management>device manager>double click on display adapters, it will expand and show you what is installed. If it doesn't expand you do not have a chip set. If it does after installing the 8800 then return to the device manager and attempt to disable this chip set. It may or may not disable. How this is done: start>control panel>administrative tools>computer management>device manager>double click on display adapters, it will expand and show you what is installed>right click on this item a click disable. If it will not disable an error message will appear.
Enjoy! I think you'll be happy with it.