Group Policy - User Rights Assignment

I have a small network with Win 2003 Servers. One of them runs BackupExec. It is a stand-alone server. Apparently I can't perform windows updates on this server. Googling the problem showed that my administrator doesn't have the rights to

1. Back up files and directories
2. Restore files and directories
3. Manage auditing and security log

Under Group Policy - Local Security Settings - Local Policies - User Rights Assignment I can find these rights, but when I open them up the "Add Users or Groups" button is grayed out. I have tried this from the stand-alone server and from the DC (using Group Policy Manager) without any luck. The sole user who has these rights is "veritas", the user set up for Backup Exec. I vaguely remember giving him the rights but don't remember taking them away from the administrator although I must have. Does anybody know where to go to actually edit these rights?

Thanks

LOCO lobo