Personally, I don't care for prefab computers. There's always a corner to be cut in the quest for the cheapest deal. if you know someone who custom builds computers, I think you'll get the best bang for your buck.
This is also my opinion, but I wouldn't go with Pentiums. They're more expensive and (in my experience) more buggy. After my PIII 1 Gigger, I'll never get another Pentium CPU EVER again.
My origins have been clouded in mystery... some say that I was once a man, known as Hamato Yoshi. Another tale states that I was once merely a humble pet rat of a man named Hamato Yoshi. For the record allow me to state that both are true... and yet, neither is true. Such is the way of Ninjitsu.