i wud recommend norton 360 v3
It installs in seconds and is a full featured pack. It optimizes ur pc, an integrated backup manager, startup delayer, a vast features for improving system performance including registry cleanup.
There r 2 types of virus scan..
1. quick scan - which scans the potentially dangerous folders. It wud complete in few minutes.
2. complete scan - checks ur pc throughly 4 virus, spam, trojan etc
There is also an add-on pack that gives much more features.
BUT WAIT, ... NORTON 360 V4 IS ABOUT TO COME.....