We're about to get a dedicated server but we're on a tight budget. Is virtuozzo control panel really necessary?
I wouldn't say so. Even if you used OpenVZ with HyperVM, your clients won't complain (as a lot of hosts use this already)
Are you wanting to offer VPS? If so, OpenVZ and HyperVM would be fine. Now, VZPP is a little more flashy and professional looking, but it really doesn't matter. I think functionality is more important anyway. If you are not going to sell VPS's and are needing a virtual solution for your own use, try Vmware Server. That's what I use for many uses. It's free, but you can't use it for commercial purposes.