Yes. You can go the Home Depot route and build your own. You can disassemble the ballast set up and just mout the endcaps to your hood so as not to take up space.
Based on your question about wattage and using a metal hallide, are you considering keeping light dependent animals in the future? I don't know much about MH
lighting, so that aside, if you are thinking of keeping an anenome for example, you might want to forego the Home Depot project and just purchase a VHO
ballast for your 29. That way you could mix an actinic blue and a 10,000K giving you 50/50 lighting at 130 watts. This unit is a good deal and worked great in my 29: http://www.hellolights.com/2laaroasbaki.html
Also, hellolights.com has the best deal on bulbs I've been able to find. My LFS
bulbs for almost double the price.
But, again, I'm just assuming that this might be something you are interested in. If not, please disregard...
As far as a fan goes, I believe that if your hood is open you don't need one but it couldn't hurt. But definately if you have a closed hood I would, especially since I'm under the impression that MH
bulbs give off a ton of heat.