I am so going to do that this winter when I get sick. (Always a matter of when. I work in a casino where everyone can smoke inside all they want ) Something so simple that I couldn't figure out. Go figure, hehe.
However, back on tipoic, I was at an ROTC military camp back when I was in HS and came down with a fever. Had to get up at 4:30 and PT, so I know what it is like. GO ahead and do cardio, but don't push yourself too hard. Cut down the distance/time you run/spin/whatever and drink alot more fluids.
If it gets harder to work out than usual, then stop, even if you barley started. Better to lose a wee bit of progress (if you lose any) than to oush yourself too hard and hurt something.
Hope ya feel better!