We already have a high powered, windows 2008 server all completely configured for our domain.
We want to add HPC abilities to our server. Does this require to install a new server ontop of 2008 or can HPC be added onto it?
Windows HPC Server is designed to tie multiple servers together for use computing data intensive applications; I'm not sure that sounds like the workload that you are trying to address.
I'd recommend taking a look at one of the product websites for more details: