i used mv lights (175w, just like you have there) with little success. i'm assuming you are growing from seed so, here's what i did... maybe you can follow my lead.

and btw, mh uses a different kind of ballast, however, the only difference between an mh and an hps is the hps has an ignitor, the mh does not...

http://www.onlinepot.org/grow/wiringlights.htm

3 mv 175w had very little effect on plants, and caused major heat probs. i went to lowes and got a double 48" flourecent fixture for 12$ and two GE daylight 40w t12 (3050lum ea., 6500k) for 5$ ea. these produce very littles heat, so the lights can be right on top of the plants, even touching without any burning...

immediate turnaround on the veg cycle, i've not had as good of results outdours as i had with these lights! ended up having to add another double, but they're amazing for veg.

if you are starting from seed, you'll have 4-8 weeks before you can flower your plants (they have to reach sexual maturity before they will show sex). that should give you plenty of time to get a ballast. i don't recomend anything less than a 400w though...

if you can find old used security lights (fleamarket, junk yard, lowes change out...) they are generally 400mh; you can convert these by purchasing a 50$ ignitor.

hope this helps...

love, kp