Is it safe to run AVG and AVAST at the same time, or will the two AVs conflict?
Listen to the others but, if you want the exactly answer, it's
yes, you can have avast (resident) and AVG (not resident) running at the same machine (XP SP2). But, please, look your steps: you're doing a 'dangerous' thing that you must know what you're doing. Take care of both email scanners at the same time. They work togheter but you must know how to configure them...
I'll recomend BitDefender (free) or AntiVir (free) as a second, non-resident, scanner.