I posted a thread before I started growing about fires caused by HPS bulbs, and most said it won't be a hazard unless it falls. It definitely won't start any fires though just from being on, but don't let your room get over 85° or the plants will be stressed. I run a 1KW HPS over a 2x4 area and I use a squirrel fan to suck air straight up off the bulb through the top of my DIY hood, a small 5" fan blowing across the bulb, and a large 20" fan blowing up into the hood to circulate air and a 20" box fan pulling fresh air into the room through a filter. My room stays a bit on the cool side, 70 with the door open and around 75°-78° closed and the low 60s at night.

Also, you can get a Brinks digital timer at WalMart for like $9. Thats what I use to run my lights and pumps and they work great. They also have a built battery backup in case the electricity goes out.