If it's a Microsoft file (check it's properties) it's not, if it's Nimda.E
then it's a virus. These files have had some viruses that appear to run as
the legitimate processes.
If you're not sure about a file, Google it. You should come up with
additional information on them.
csrss.exe and smss.exe should be in Windows\System32 folder and should show
Microsoft info on it.