I have a dedicated server, currently i sell shared hosting on this server... Now i want to sell VPS also on my server. Is there a way i can sell VPS? Can i use Xen Hypervisor,will it disturb my shared hosting accounts and settings ?
XenServer (ESXi, Hyper-V Server, etc.) is a type 1 bare-metal hypervisor: you can't install it on top of another operating system. You might have some luck with VirtualBox, depending on what you want to do, as it's a type 2 hypervisor and runs on top of a host operating system.
You may also have luck using something like chroot or BSD Jails (depending on what OS you're running; you didn't say) to give your users shell access and isolation.
Not to sound offensive, but given your (likely) lack of knowledge in this space, I would strongly recommend NOT going down this road. It's one thing to charge for hosting a few websites that require perhaps FTP access, but when you're getting into VPS, your customers are going to expect a certain level of quality of service (perhaps even an Service Level Agreement) and you may be biting off more than you can chew.