I got some mail some time back about eMachine upgrades that I never got around to posting. I’ll just summarize because that’s easier (it keeps me off the mouse).
First off, definitely look into a new hard drive. You can pick up a 7200-rpm drive of decent size (10-15 gig) for under $100 these days. I’ve had trouble getting Western Digital drives to work with older disk controllers, but no problems with Maxtors, and I get better performance and reliability from Maxtors anyway.

Next, eMachines tend to have problems with their power supplies. Get a replacement from PC Power & Cooling. It’s $45. Cheap insurance. And chances are the hard drive will perform better, since the PCP&C box will actually be supplying the wattage it claims to supply (which may or may not be true of the factory box). And remember: low-cost PCs have always had skimpy power supplies. Commodore and Atari made great low-cost computers 20 years ago, but they had horrendous power supplies. Given a properly made third-party power supply, a Commodore or Atari could run for 10-15 years or more (and often did).

Finally, get 128 megs of RAM in the system somehow. If you’ve got 32, just go buy a 128-meg stick. If you’ve got 64, get a 64-meg stick or, if you can afford it, get a 128.

Since eMachines have pretty wimpy integrated video, you might also look into a PCI video card with a Matrox, nVidia or 3Dfx chipset. Matrox gives slightly better 2D display quality, while nVidia and 3Dfx give better speed with 3D games. If you’re into gaming, definitely look into a new card.

That’s the strategy I follow with any upgrade. Get a modern disk in there, then get more memory, and replace anything else that seems underpowered. Do the disk first, then deal with memory, then possibly the video. Then, and only then, do I start looking at CPU upgrades. I’ve turned 200-MHz junkers into very useful machines again just by adding memory and a fast disk. The CPU isn’t the bottleneck in most systems.