Buy a copy of Norton Antivirus Corp edition, set it for autoupdate every 8hrs and then sit back and enjoy your comfy life.
On that note, buy a laptop you can take it everywhere you want, enjoy the freedom it offers and be portable and reliable, the price you pay for a computer for what you appear to be doing is going to be the same price as a good laptop.
Recommendation for good laptop:
1. IBM-T20 series
2. Compaq- Armada series
3. Sony Viao-I have the 580
Get something rugged, sturdy, and something a business would buy not a cheap home imitation. Afterall you think that a business will rely on something breaking down all the time? Steer clear from gateway's and hp's. Dell's are decent but I would aim for a Armada or a T or A series from IBM.