I would think a PowerEdge 2950 or the like would be good. Thats a rackmount.

 

If you're only going to use it for DNS, DHCP and a domain controller, 2 73GB drives in a raid 1 should be more than enough disk space.

If you also want to store user profiles and things like that it becomes a whole different story. You'd first have to decide how much space you want to give to each user for their profile and things.

Depends on your environment, but for small clients without filtered air, I generally go with full size servers due to dust buildup/heat, generally full size server give more expansion possibilities. For 60 uses I would go the 2900III, quad core 3.0, 8-12 meg ram. Disk size, as Dev points out it is your decision. The newest 29000III I placed for a 30 client system running Windows 2008 Active Directory is comprised of (2) 73 gigs as a raid 1 for the OS/programs, and  (4) 73 Gig drive raid 5 for data , 1 global hotspare, all 15k SAS. The raid 1 size is far more then I need for the OS/programs, but I will use the space for archive; all the drives at 73 Gig allow for a global spare. I project the arrays will use 2/3 of the space in 7 years; I do not like approaching array capacity.

The server is the Active Directory FSMO, DNS, DHCP, WINS, File services and is the main file server. Runs Great Plains 10 and another SQL database (SQL 2005), BackupExec, Symantec 10.2, Perfect disk 2008, Anti spyware software, Dell OpenManage, all the AD tools. The server is fast, all services and resident programs do not bottleneck this server.