Dude,
This question is just such a big can of worms...
For your MPC you will need a Zip Drive for your PC (to transfer samples), Soundforge (to cut up samples) and perhaps something like Recycle is good too..
If you wan't to record on it and you are serious...I would steer clear from a Compaq or any generic brand they tend to cause all kinds of conflicts with Pro-Level Sound Cards and USB problems and the like, and are made cheaply as a whole including onboard sound & video which you might not be able to disable and are less upgradable for this reason (say in 2years you need to add this or that) However some people can get them to work fine...
Best method is to say right...I wan't a Delta 1010 or Digi001 and then search the web for people who have those Sound Cards then cop the same system they have...Eg: Motherboard, Memory, Video, HDD etc...
Plus, you are going to need some software too...Logic, Cubase, Nuendo, Protools, Sonar, etc... and there will be many tweaks and stuff to get it all running smoothly...
Here is a old link with the basics:
http://www.studio201.com/cwu/support/vs ... tions.html
Try other forums like
www.futureproducers.com