MH pendant help?

[Gatorbait]

I'm trying to set up the lighting for my 20L and I've got some choices and am looking for opinions. I've got two Regent halogen light fixtures that I'm planning to use for housing, one 300w and one 500w. I was told that a 70w DE would fit in the 300w housing and a 150wDe would work in the 500w with a little modification to the socket. Which one would you use for this size tank? I plan on only using 2/3 for display and 1/3 for sump area. What ballast and where can I find one for a good price? Preferably electronic. Will the icecap 175w work with a 150w DE? How about bulbs? I'm pretty handy with a dremel and wiring, I'm just having a hard time keeping all the ballast and bulb combinations straight. (M57,58,59) Thanks