Yeah that's not enough light for hardly anything except mushrooms and zoas... Sorry. I would keep looking for something more powerful. T5s are cheaper and give you more bang for the buck than MH if price is the issue.
I was planning on keeping some anemones, but low light anemones. What about corals? Anyone have suggestions on what types can be kept with 150 Watt metal halides?
300 watts of MH on a 120 g fish tank, you really won't be able to keep much... Most things require a minimum of 4 wpg. Anemones, more like 8 to 10. I know, watts per gallon is not a hard and fast rule, but we're ballparking it here, guys (Freak...).