Hi Beachyb
Luckily I just found out the answer to this last night. I downloaded a lot of new sound banks and really needed to get this sorted to test the new sounds.
Well I use Cubase 3 SX and it's really obvious if you think about it
After loading up the Virus in the Instrument List (see attachment 1) you simply set the In/ Out of for the track to be the Virus on the Instrument list (see attachment 2).
I also had to switch on monitoring (in track controls) to hear anything (see attachment 3).
Hope that helps!