Linux can run on any bog-standard PC.
You don't need any special specs unless you need higher performance/reliability.
Personally I use two boxes (mainly, there are others obviously 🙂 )
Both have two Celeron 400MHz CPU's on a ASUS BP5 dual board.
One has only IDE disks, the other also has 2 SCSI disks and an HP tape unit.
SCSI is provided by a cheap NCR controller. Network comes from two 3Com cards (hurricane or something, I forgot the exact name)
These machines give greate performance for their price.
But ofcourse, they have zero redundancy, so not very suitable for mission critical applications. But they are great for testing, developing, gaming and non-mission-critical hosting apps.
And they won't reduce you to poverty.
If you are just going to develop and test, I'd go for something AMD800MHz or 1.2GHz-ish(depending on your cash-situation), with at least 512MB RAM (RAM is a synonim for speed) and a single 20-40GB disk is more than enough.
You'll have to peek at some websites to see what kind of motherboard is preferred.
In short, you don't need a $2000 machine to run linux (unlike some other OSs...).
