My two penn'th...
I have two machines, both P4s running XP Home and networked.
On the lappy I use
Vet.
On the desktop I use
Trend Micro's PCCillin 2003.
Both are supplied by my employer, so both are registered and auto update seamlessly. Both are excellent. Most time the machines just check themselves, but occasionally I do a manual scan, using one machine to cross-check the other. So far, according to Vet, PCCillin has not let anything slip through, and vice versa.
AA