go to friggin
www.ka24dedevelopment.com and read orion's massive page on VLSD"s and what fits /doesn't fit
You should really get as much seat time as you can now , open diff or not. When your skill level has improved, you will be able to take ful advantage of any diff you get.
As for HLSD's...search, there are plenty of good threads on them. They are taken from s15 silvia Spec R's (or u can spring for a Quaife$$$$) and you put the internals and output shafts into your existing open diff pumpkin
you know...good tires improve grip levels too