You should have a look underneith the bike to see if the clamp brackets are still in place for the center stand. If the stand has been removed, than maybe the remover cut off the brackets too. Might be some pics on here somewhere but basically they look like two brackets with about a one inch hole in them and they are sloted to work as a clamp.
If you have the brackets then it's a simple matter of getting all the hardware to bolt it on... and the center stand itself.
If the brackets are gone.... well, we will worry about that when you find out if they are there or not.
Matt.