PEF said:
Is it valid to install 2 antivirus instead of one? in this specific case
AVG and AVAST, will they work well together? or will inhibit?
It is generally unwise to run multiple anti viruses and firewalls. Such
programs may conflict (try to fight each other), and cause performance or
connection problems. In most cases things work out, but I really do not
think it is worth the risk and the slow-down. Uninstall one of them.
If you feel a need for a second opinion, you can download and run another AV
software or try an online scanner every now and then. Beware that online
scanners are advertising tools though, they tend to exaggerate positives.
Vista is a pretty secure OS, keep it patched and exercise sound judgement
when online, and you should be OK with the one AV.
Charlie42