Sounds like you urgently need another virus scanner, such as one that actually gets rid of them!
Turn off the modem. Reboot all machines into safe mode and virus scan, plus run hijack this to see if there's anything weird going on.
When thats sorted or as much as you can, reboot the modem.
I often wonder how companies cope when they get viruses.
I'm sure you know this choj please don't take offence. I know how stressful it can be.