Yep, that's right. In fact the whole package cant get off the ground without the SRB's, the mains(fueled from the big orange tank) all burning together. Then releasing the SRB's as they burn out and continuing on the main engines on a nearly flat trajectory for some time to reach orbital velocity.

But then though, as Deathcoffin said, it would be cool to be able to fly it as a conventional aircraft, unrealistic as that would be it could be done because we are after all just running a simulaton that can be programed to do anything we want. Heh, just for the fun of it if nothing else. :P
Back in 2003, I took part in a thing called "Battle of the Airlines, Mission Moon" and in it we recieved an add-on model of the space shuttle which had two models with it, one with tank & boosters and one without. I could fly both like a conventional aircraft if I so desired and it was quite a sight to see the full package flying along, Orbiter,tank & boosters all together. And was fun to do just for the heck of it. 8-)