Can i install anti-virus software when i already have a virus?

Im assuming its a virus or spyware/ malware etc etc. I unistalled AVG because i was going to put Norton on and completely forgot...Anyway I've got somthing nasty on my comp and when I run spybot its showing that I've got absolutley s*%t loads of rubbish on their. Same thing with ad-aware.I immunize them but when i re-run spybot its still there. i figure I need to turn off system restore and go in safe mode and do this again but what do i do about having no antivirus software? Can I install it whilst in safe mode? I have a good copy on disk.

Also, can this virus be spread through my wireless network?

Can i install anti-virus software when i already have a virus?symantic

Many viruses will block the installation of antivirus software. Since the virus does it work within the copy of Windows it installs itself to, the safest way to remove the virus is to do the following:

1) update the antivirus software on a PC that's not infected.

2) remove the hard drive from the PC.

3) place it in a USB external enclosure.

4) connect the enclosure to the clean PC.

5) run a full virus and spyware scan of the hard drive using the highest scan settings the security software provides.

6) if needed, connect to housecall.trendmicro.com and run a second scan to verify that the virus was removed by the initial scan.

Can i install anti-virus software when i already have a virus?viruses