I upgraded my PC and it was well worth the money. For around $600 I have a new PC. I never suffer from disk space so that was fine, I stayed with my 1GB of RAM (which I may bump up) and the only things I changed were the CPU, Graphics Card and a new internal DVD writer.
I upgraded the main CPU from a Celeron 1.7ghz to a normal Pentium 3.2ghz. Amazing difference. My test was simple, a screen I have been working on in TrueSpace 6.6 took basically 8.5 minutes to render in full quality mode. With the new CPU it takes only 9 seconds. This is a huge difference in productivity
I then went away from the GeForce 400M to the new GeForce 7800. This bad bear is pretty amazing coming in at 256MB and AGP 8x. I had to stick with AGP because the motherboard does not support PCI Express
Lastly, I upgraded to the Plextor PX-716SA 16X Int Dual Layer Sata Drive (P67-1118 ). This drive is highly rated and only costs $100 (before the rebate).
So in short, I am glad I bought a good enough motherboard years ago (ABIT) that supported the full range on Pentiums for the 478 model.