How to best set up a xp network

Hi guys

I’m actually a coder and not so much a network admin. But I’m helping my girfriend’s dad out with there network he’s got about 8 computers on a Win Xp and a ADSL line, I had a look this weekend and I have 3 questions,

First I think they need a good antivirus software what do you guys recomend?
Second do you think I should set up the built in XP firewall on there machines or set up a software Firewall on a machine? and have the router after it?
And third how can I set up to have machines to update regulary so i don’t have to come and do it every week?

Regards
crit