Ok, so i have used linux based labs to practice network hacking for a while now. But now i want to build a virtual network that will emulate a windows enterprise network, i currently have set up a DC/DNS server a web server i intend to put vulnerable asp web apps on i also set up a SMB share server all in Windows 2003 R2 and i will add clients varying from XP SP3 to Windows 7 and vista (to simulate the ever changing landscape of a large network) i will add Cisco IOS gns3 vms and i may add a UC/VOIP system running traffic generation scripts. My question is what other services or network appliances should  i add to make this as realistic a lab as possible, keep in mind that while i can run VMs of alot of things i am on a student budget so alot of hardware components are not available to me. Thanks in advance for what ever advice you may give.

based on the resources available to me and my goal to stick to M$ products i will go with MS SQL server may add fake spoils as entries in the database now that i think about it, i also will add a fedora Snort box because from what i understand that is a common IDS setup, and how could i forget? a Mail server?!!  i may add actual mail accounts and internal emails for lulz and realism sake maybe a sharepoint like you said any one else have any ideas?

no

thanks i will add a exchange server and i may go the office communicator route for VOIP and have clients with softphones running traffic generation scripts and a MSSQL server i don't have much experience with sharepoint so it would make a good learning experience i may also add a VPN server as that is always a good way into a network.

As 3xban said implement PKI and kerberos as well as that is common in enterprise networks. Also there is DHCP, the System Center set of products like config manager forefront endpoint protection, WSUS, WDS, RRAS, Terminal Services, Branche Cache, there is a ton more services and features to add that would be useful but thats just a start.

Check the vmware appliances list at their site, their might be a free snort virtual appliance available.