Dude, just grab a 512 stick of ram, or even a 256, and a GeForce 6600, or Radeon 9600, or better. All can be done for well under $100us. It's your video card mostly that's hurting you, I had one of those and it was the most awful card I'd ever owned.
These two video cards are pretty old now, but more than enough for LFS, and would have been great cards when your PC was new. The GeForce will be a lot easier to find btw. Even a 7600GT can be had for very very cheap and would triple your frame rate.
P.S. More ram will never add to your frame rate, only prevent stuttering caused by disc thrashing when you're running too low on Ram. Only "faster" memory will have an effect on frame rates, and even if you somehow could put the fastest DDR3 memory on your board, the difference would be negligible, with respect to "LFS".