You should do like I did and join a local Microsoft user group. At last month's meeting they had a drawing and were giving away a few copies of Windows 2003 Server Enterprise Edition(scalable to 8-way CPU) with 25 users! :Q I happened to be one of the lucky ones!
It's an NFR but not crippled in any way. I had to do a registration process, so the product is tied to my ID(so no sell or copy), but what the hey - now I've got a nifty legal server license to play with for the domain at home.
As for speed, I've got it running on an XP2500+ with 512meg DDR and haven't noticed any speed difference as compared to a similar system running Win2K Pro.