NO operating system no matter who produces it is Bug Free, this is why there are continous updates, however Windows 7 RTM is extremely stable. So far all the software I used with XP pro has worked with Win7 just run with elevated privileges and your software should work fine.
For Antivirus there are several available that do a fine job.
Microsoft Security Essentials (MSE) is working very good for me on one machine
Avast Home Version 4.8 works well on anoher machine
Avg is doing a great job on my laptop
Anti-Vir is working out on another test machine.
Hope this helps answer your questions...
is the rtm version now bug free as i am currently on xp but does all software work with it i like xp does plus whats best antivirus