First off: Do not ever buy an eMachine ever again. :P

Second, if you know someone technically inclined IRL, get them to put together yer stuff for ya, or buy the parts cheap(custom built is always more powerful and cheaper for the same/better power than any prebuilt brandname shit, always.) and pay labor at a local computer store to set 'er up right for ya. I'd suggest some specs but judging from what you said it probably won't help alot; just make sure you get at least 2gb DDR2(NOT DDR, make sure it's ddr2) ram, a Quad-core processor(if you wanna 5box on one comp, you gotta go quad, dual won't cut it.

I also personally prefer AMD over Intel, but either should work); and I personally recommend going with Nvidia video cards, 7900 or higher, preferably an 8800 as that's the best bang for your buck on the market right now; I'm not a fan of ATI whatsoever, and Nvidia's products have always worked well and lasted me long enough ;p Plus it's easier to keep track of their upgrades via the numbers, an 8800 is obviously better than a 7900, whereas an ATIXVQRWTF could be better or worse than an ATVXBBQLOLZ, I hate their numbering system lol

Try to get a SATA harddrive if you had an IDE one before, as that'll help some speedwise. I have a SATA but I've been too damn lazy to hook it up since I bought it months ago, still using an IDE >.> And make sure you get a power supply that can support it all, at -least- 500w, maybe 550-700 for added protection. It's really not all -that- complicated to do Hardware, it's mostly connecting wires and screwing drives in, the only trouble you'd have is if the drive is brand new and you need to install & update windows/drivers/etc which can be a pain in the ass.

If you still would prefer non-customs, honestly, I don't know who the "reliable" names are for prebuilt nowadays; I don't hear alot good about Alienware anymore, and I'm not sure how well Northwest/Falcon/whatever it was is doing nowadays. I'll leave those suggestions to other posters ;p