yes, you can split the 240 line and make it two 120 lines to do anything you want with. however, it'd be much easier if you just use your line the way it is and run your ballasts directly from that line. most ballasts are switchable, you just need a 240v cord and you'll probably have to wire a new receptacle.
be careful though, playing around with electricity is very dangerous. have a trusted friend who knows more about these things give you a hand. if you don't know anyone, hang around an electrical contractors shop, and wait for people to get off work and offer them a side job, say 50 bucks. better to have someone who knows what they're doing do it rather than burn down your house or zap the shit out of your heart.
Good luck though, oh, and a sidenote about using 240v lines.... they have much more amp capacity, and as such generally are cheaper to run. in a house the difference is almost negligible, but if running lines over distance, much more noticeable. Hope this helps!