Hello,
I agree with above suggestions.
Adding to above, also check this :
About using Backup Exec with Symantec Endpoint Protection
http://www.symantec.com/docs/HOWTO22991
So, overall, when installing SEP and Backup Exec on the same machine, you would have take care of 2 things -
1) Ports used by both.
2) Make sure you have enough Memory on the server.
Hope that helps!!