I agree with Virtualization (really, it is a must for any lab).
If your budget is low, crank up the specs on your desktop machine, and use VMWare Workstation (or some such).
If you budget is a bit higher, get that machine and dedicate it with Xen Server or vSphere (or whatever)
Higher yet? Get a couple of boxes, and an iSCSI solution so that you can support clusters (iSCSI is much cheaper than fibrechannel, and you can do windows clustering as well as your virtualization platform clustering.)
You want brands? I did it with generic computing hardware (24GB core i7 boxes) and a Thecus iSCSI solution (because I didn't want to take the time to build the iSCSI myself). WD RE4 drives. Get funky with quad-port Intel NICS and a linksys switch that supports VLANS.
Make sure to get a Microsoft TechNet subscription if you are working with Microsoft platforms.
Gonna grow it? Start with VMware Workstation. The VMs you create can migrate to dedicated virtualization platforms as you move up in expenditures.