think you might have trouble fitting it, less you aint using a reflecter, such a confined space could get pretty hot you would need some fine ass ventilation double up on fans
Your main thing will be heat.. I've got 70 watts of cfl in a mini tower and it hits 85F.. (67 in room).. 3 120mm fans, 2 80mm fans.. should note that it is stealth though, ZERO light leaks allowed so the air intake is tricky..
If you have the ballast remote placed I'd bet you can manage it.. i've seen a REALLY good pc grow with a 70 watt hps scrog before.. cant seem to find it right now, but it is possible.
Yea i had considered doing it with a 70w ceramic metal halide from phillips.. but it was gonna be $150 just for the light and bulb.. its just my veg box so i went to cfl's instead