Do you have a router? If not then get one, hackers will find it extremly hard to get past them.
AVG for windows seems to sugest that it will be compatible.
Chances are, most of the dangerous loopholes haven't been discovered yet. (Not guarenteeing this, as I haven't looked into anything about Vista's security.)
Cisco CCNA, Comptia A+, 1/3 through CCNP