apologies for not replying earlier
i ran the kaspersky - it took for ever, because it kept stopping to ask what to do when it found something - it didnt find anything that other progs hadnt already found (i hve a few files on my pc which give false postives in all anti-virus progs)
i now only have the whistler virus in the mbr of my non-bootable, usb hdd's - as far as i can make out, it isnt a threat there (as long as i dont boot up from them), so, since i cant find any way of re-writing those mbr's, i'm going to ignore the presence of the virus
i thought i'd outline what i did to remove the virus from my internal, bootable hdd, just for anyone else whose avast tells them they have whistler
1. download and run mbrcheck to confirm its in the bootable drive(s)
2.download and run BTKR_RunBox to re-write the mbr on those drives
it was , in fact , extremely easy
unfortunately all the mbr fixing tools seem to be command line, which i know nothing at all about, but which, i think, doesnt work over usb connections - so you cant clean the mbr of usb drives, but if they're non-bootable (no OS installed on them) then i dont think it matters (fingers crossed!)
thanks to essexboy, and everone else for all the help!
chris