I got these lights from Murray's for christmas one year...
http://www.murrays.com/mm5/merchant.mvc ... re_Code=MS
You can purchase cheap carabiners from a harware store and clip them to your bridle or the tips of the hulls and one on the boom or rear crossbar.
As for legal concerns, I understand that you have to have at least one light that can be seen in all directions. This is either for boats that are not under power or under a certain legnth-I can't remember. I tried this once with a aingle light I bought from West Marine.
When a power boat aproached us I heard a voice say "Isn't that a sailboat, and shouldn't they have lights on? The sail and our bodies were blocking the one light. I did shine another light into the sail though and then turned around to go home.
I purchased these in hopes that my friends would share my enthusiasm for sailing at night. I have yet to find one. However, I do plenty of night paddling w/o lights and have a great time at it.
-good luck and Happy (night) sailing.