First you'll need to decide if you want to use Hyper-V, or VMware (which are the two major choices) or one of the smaller platforms. Then you'll need to add up all the resources that the 10 guest OSs will need. If each guest needs 2 Gigs of RAM then you'll need 20 Gigs of RAM for the guests (and 1-2 for the host). Same goes for the amount of CPU power and disk IO. If you plan on adding more virtual machines later on then you'll want to plan for this now. Any server that the major vendors will sell will support virtualization.

First you'll need to decide if you want to use Hyper-V, or VMware (which are the two major choices) or one of the smaller platforms. Then you'll need to add up all the resources that the 10 guest OSs will need. If each guest needs 2 Gigs of RAM then you'll need 20 Gigs of RAM for the guests (and 1-2 for the host). Same goes for the amount of CPU power and disk IO. If you plan on adding more virtual machines later on then you'll want to plan for this now. Any server that the major vendors will sell will support virtualization.