Trojan won't allow boot into safe mode

Hi all -- i've managed to cause more throuble than I solved --
attempting to repair a friends PC that was LOADED with virus/trojans,
but it would not let me boot into safe mode (it *would* boot normally
however, but when trying safe mode it blue screens and recycles).
Trouble is I thought I could get around it by setting /safemode in
msconfig -- bad idea as now I can't boot normally and safe mode has
the same issues, so I'm in an endless boot to safe/blue screen loop --
does anyone have any suggestions?? Thanks