How did SP2 trash the PC?
SP2 contained a bunch of enhancements to improve overall security, the forthcoming SP3 rolls in even more.
If you've got decent firewall and AV and most importantly, act sensibly, you'll probably be fine.
www.microsoft.com/downloads/details.aspx?FamilyID=049c9dbe-3b8e-4f30-8245-9e368d3cdb5a&DisplayLang=e n
is the link to the full SP2 download rather than the 'clever' installer that just tries to download the bits you need to update to SP2 - you'll almost certainly have more luck using this than the other version.
Might be worth waiting until SP3 comes out.
Like OD said - if you're using a router then they'll almost certainly be locked down tighter than the proverbial ducks arse - if the firewall on the router is dropping any packets that don't originate from inside the firewall then all you have to worry about securing is the PC. That's where proper AV solutions come in - preferably something that will integrate with whatever email client you use.
AVG gets loads of good reviews but if you want to be really safe go for something that's been properly certified and has proper research funding behind it but comes out around average for overall protection..