You did not mention if this VPS is running a Xen kernel from the host or which provider you are using. Most XEN VPS providers utilize a kernel (selected from a list) in a web interface in the hosting providers web interface. To use a kernel module that is not already present in the kernel will likely require running a pv-grub configuration. Your provider likely has documentation for this.
A good indication of how the running kernel was built is looking at config.gz
Also, if you type lsmod and nothing shows up, this kernel was not likely built to support additional kernel modules.
You may also wish to look through the community forum of the VPS provider that you use. They often have a FAQ or forum that covers provider specific limitations and workarounds.