How to do this?
 

I have a string part in cubase sx3 which is on ewql symphonic orchestra software, and I want to send the strings into the virus so that i can add an lfo to the pitch of it, and maybe put some of the virus's effects on it. Is this possible? if so please explain how to do this, as i can never seem to work out how to send audio into the virus from cubase..

You cannot modulate the pitch of incoming audio. You can modulate a filter with an LFO to process your audio input. You need to sample your strings and then play it on a sampler with an lfo modulating the pitch. Since the pitch will effect the timing of your phrase, I'd listen to how it comes out and then resample the strings so that the timing will match appropriately, in terms of phrase length.

The audio inputs don't run through the oscillator and pitch stage. Only the filters, amplifiers, and the effects, etc.

However you could fake pitch modulation by running it through the Virus' chorus effect (using something like Dir/Eff = 127, Rate = 110, Depth = 127, Delay = 35, Feedback = 0, Shape = Sine). If you want a blend between the pitch effect and the original, just set Dir/Eff to your choice.

You can also go one further and set the audio input to dynamic mode (meaning you use the Virus keyboard as a gate/envelope for the incoming audio), and start using the modulation matrix to control the Chorus settings (along with any amp and filter envelope settings to be controlled via the Virus' keyboard).
If you get clever, you could also use the matrix to map amp-attack time to chorus wet/dry, for a fade-in of the pitch effect, etc.

Ideally, however, just use your ROMpler synth engine. I'm sure your orchestral VSTi would have been bundled with one, or you could dump the samples into a sampler VSTi (Kontakt, Halion, etc.)

you can turn the virus into atomizer mode and using midi CC settings modulate the pitchbend wheel in your sequencer to control it like an LFO