The best thing is to have someone with experience to lend a hand but failing that have a look at some of the videos on this page for heli setup, really helpful:
http://www.helifreak.com/showthread.php?t=41692
I've got a 450 size heli that I've been flying for the last couple of years (prior to that years earlier I had a Hirobo Shuttle, it had a mechanical gyro that's how long ago it was) and use a DX7 although my brother has the same heli as me and I set his up for him on a DX6.