First, I should point out that you should be REALLY careful with the processor as installing the wrong kind will most likely kill your motherboard. Personally, I would not get a processor off of eBay unless the seller was willing to send me hi-res pictures of the top and bottom of the chip.
As for the memory, you should make sure that all of your RAM stick match eachother for best performance. If possible, buy 2 (or 3?) of the exact same stick from one vendor. Mismatch RAM size almost always results in poor performance.
You should definitely upgrade your graphics card if your motherboard will support it. I recommend something from the nvidia geforce line using a pci slot. Once you get accelerate video working, flash shouldn't eat up as much memory. With a good enough graphics card, even old clunker systems can run compiz (with very few plugins).
Also, if I'm following these posts correctly, your machine is too old to run Fedora 11. I recommend Debian Etch with LXDE ultra light desktop. Not as many bells and whistles as GNOME or KDE, but the Openbox window manager that it uses is very configurable. Through a little tweaking here and there, I was able to get Firefox 3.5 to play vids on youtube with just under 256 MB of RAM. You got to turn off all the system services you don't use and try not to do too much at one time. It's also very important not to exceed the manufacturer recommended max memory.
If you don't want desktop icons, you can also go with straight Openbox, but you will need something like Tint2 to hold apps that run in the system tray. Also, if you don't need all the extra stuff that NetworkManager does, you could try Wicd in it's place. Or you could learn how to connect to a network from the terminal.
I hope everything works out for you and welcome to the world of Linux. I got the impression that you were a newbie.