might be my XP tendancies making me over paranoid, but Id be inclined to get the AV up and running and give it a scan.
Whenever I install Windoze my installation order goes
drivers from disks > Firefox > AV > Firewall > windows update > other software.
This stems from the bad old days when an unpatched XP machine would be infected with something within 30 seconds of going online
You can run standard Windows Firewall and Microsoft Security Essentials (free with Win 7, which you can update to a better version online for free) and be totally safe from virus/malware.
Drivers from disks are no longer needed in most cases as Win7 will detect and install for most items, ive been running this machine since Win7 and only installed an updated RealtekHD driver.