You can install your own Virtualization engine yourself. Xen and OpenVZ, you could install on virtually any server. If you're thinking on offering VPS and don't know how to even set it up, I would suggest against it, at least until you learn to setup and control your own environment.
This also goes if its your own VPS environment for yourself. Start wit vmWare server (its free), and then you can jump on Xen or OpenVZ.
i have just purchased from burstnet server with additional fee to install Xen OS as main operating system. but sadly, they have no good support for this, i got networking problem for 7 days there is no resolution until now