I'm thinking of getting her the HSU Ventriloquist with an SF-1 sub ($498 total), and then a used Yamaha or Onkyo receiver.

Any other suggestions? I can't get her something with a large sub, since she lives on the second floor. In fact I even considered getting her just the Ventriloqist system, which cuts off at 80Hz, but I think that would be a bit weak...

Try to get a receiver that has 6 or 7 amplified channels and then run the base shakers off the extra channels. mount shakers to bottom of couch/chairs. obtain bass shakers from here...<ul><li><a href="http://www.partsexpress.com/pe/showdetl.cfm?&amp;DID=7&amp;Partnumber=299-027">bass shakers</a></li></ul>

and not sitting on the couch...

Maybe I'll just get her a cheap used sub.

Full 5.1 to 7.1 speaker system with a DD/DTS (probably DD EX and DTS ES) receiver. Every major manufacturer has a wide range of them, and for an apartment it will be perfect.

Whenever she gets a bigger place and if she decides she wants to spend more cash, move this system into the bedroom.

No great deals or great quality from anyone.
I'd suggest starting with $500 worth of 2 channel gear - it'll sound way better than a HTIB system. $300 digital receiver and two bookshelfs from Polk, PSB, Boston or something similar. Then add the other speakers later.
HTIB systems last about 2 years max and get thrown away. Why settle for $hitty surround when you can have decent stereo.

I just got a Panasonic SA-XR50 digital receiver to see what all the hype surrounding the digital amplifiers was about. All I can say is that the sound coming out of this thing embarrasses my Sony ES receiver that cost 3x the price. JVC, Sherwood and Kenwood also have low priced receivers with digital amps.

like an Energy Take, or just go with the VT-12 from HSU.

5 disc dvd player/receiver, 5 speakers and a sub. installed it last night and it works great for my apartment.

Onkyo makes some really nice HTIBs, these days. They've always been a good electronics company, and they've got some awesome new stuff out.

Some of it exceeds your budget, but check their website or something like www.crutchfield.com and see what fits.