Okay, in my opinion the minimum in channels a studio should have is 8, in that case if and when you decide to record samplers direct and some keyboards or what not you have that option.
The Digidesign Digi 002 is a pretty solid unit, it runs about $1100 dollars, comes with Pro Tools LE software and is expandable (a big thing with me). The MIDI functions are getting better in PT and it is a pretty intuitive software.
The 002 has 4 mic pres on it, but they don't do much for me, I'd say you need at least a 2 channel pre, cleaner with less coloration, in hip hop you're never really going for a "sound", you usually want a clean slate for your vocal so you can do what you want with it in the box. A good pre for the job is the FMR Really Nice Pre.
Okay, for microphones, a condensor really isn't needed, but could be used, here are some dynamics that I've found to work well for hip hop.
Sennheiser 441
EV RE-20
Shure SM7
All three of these mics have an extended range over your run of the mill SM57 of SM58, and are well suited for tracking a vocal of any style in a studio.
For monitors you want to have at least an 8" woofer, the KRK V8 is a great unit... there are a ton of other choices but this is my favorite monitor for a more budget minded studio.
And for a computer, do you want to stick with the one you have, if so what is it. If you want to step up to a better computer I'd say buy a Mac. Since the G5s came out G4s are going for cheaper on ebay, you can pick up a dual 1.25 with 1.5 gig of ram for about $1500, a steal if you ask me. If you really want to go PC, do not put anything else on the computer, PCs are tempormental and they can be trouble, something I never seem to have with my Mac
This should help a little, do a search on the internet for this gear and check out the prices, also, don't forget ebay!
Later,
musik