Where can I find an online anti-virus that doesn't install on your PC?

[balfourharing15649]

I've got 5 PCs that I'm trying to use to train disadvantaged young
people. The problem is they are riddled with viruses and a firewall
blocks me from updating them. The people in charge of maintaining the
PCs won't fix them or give me the admin password (Win XP) to let me
install a new or updated antivirus the centre is being shut down in a
few months.

If they were working, I could still do a lot with them, so I've been
looking for a good online virus scan - but they all try to download a
little .exe onto your PC first, and the settings on the PCs won't
allow that.

Suggestions? Solutions? Links?

[Christopher Woods]

You might be able to create a BartPE Windows installation including a
slipstreamed antivirus program, which you could then use to boot each PC in
turn and run a virus scan to clear out the nasties. Someone must've already
put one together...

That would also obviate the need for admin credentials, because as far as
I'm aware you'd need admin privs to read files outside of your scope of
security for the logged on user :)

Any other ideas?