Multiple instances of csrss is not uncommon. I actually have two running on my desktop right now and have had more than that on a multi-user system. It can't hurt to upload the file to be verified that it isn't a malicious replacement of the normal file, but it is a perfectly common site to see it more than once.
You could also try running SFC (system file checker) from a clean boot from your Windows disk and that should check key system files of which I'm pretty sure csrss is one. (Not positive on that though.) You could also look to see if they are all running from the same windows system path. If they are running from different path's then that is a dead giveaway that something is awry.