Fluent Cantonese, but not much Mandarin ... how to begin?

[cBrammer]

Ok, so, I am new to these forums. I have been searching threw all of the threads and doing my best to dig though what resources are available. But to be honest I am not going to be able to make much of good choice without your help because I havent used the programs! Well, here is my situation and why I am asking for your help... it is a bit special. I have been living in Hong Kong for several years now and am now going back to collage, with a major in Mandarin. I am fluent in Cantonese and have about 2500 or so characters under my belt that I can read fluently, mostly in traditional, although I have been reading a lot in simplified latley. To be honest though my writting skills are not the best. Anyway... besides my collage classes which start in 2 months I want to get started early with somethign that I can dig into. What is the best programs and way to start from a more advanced position I am in? I can speak basic madarin already at rest. and taxi cabs whatever. But not very well. What can, and should I do? Thanks for all your help and patience!

Chase