How many VMs can you stuff in that box?
How to get into the VDI biz?
If your desktops are using Linux, you can use vserver with the hashify functionality to cram many thousands of VMs into a moderately sized box because all the storage can be file-level deduplicated with a free consequence of memory deduplication for binaries and DLLs (consequence of connection between inode numbers and mmap() ), so the only thing you need is enough CPU. The actual space/RAM requirements per VM (after the first one) will be negligible.
And on the desktop you only need something tiny like a CuBox to run a minimalist Linux distro (possibly running off a shared NFS root and booting off dhcp) to run an X server.