Dell has a ridiculously sick price on an entry level server.
Celeron 2.53ghz, 512mb ram and 40gb sata hd delivered for $224.
Double the hard drive size for $10 more. It's called the Dell PowerEdge SC420:
http://configure.us.dell.com/dellstore/config.aspx?c=us&cs=04&kc=6W300&l=en&oc=sc420sapp&s=bsd
At this price you'll have to add your own OS, but you can pick up an evaluation version of 2003 straight from MS for free (download) or on CD for a few bucks.
Reading books is great, but I feel there is no substitute for hands-on experience. If I didnt already have a server running I'd grab one of these. Set it up and you wont need keyboard, mouse or monitor as you can remote to it whenever you need to access it. Sweeeeeet deal.