A major problem with AVG performance problems stems from the fact that AVG installed on a workstation scans network shares the workstation uses. This really stinks. You need to define directory exclusions that list the specific shares as \\servername\sharename. Soon as we did this, virtually all of our performance problems were resolved. Bummer is, you need to create this for each client site, as it won't work to just put the logical drive letter for the network drives, it must be the specific shares.
Can you exclude the share names through the use of Profiles?