Absolutely nothing but a willingness to learn and the ability to self-motivate, really! We're mostly Perl with some Javascript here and there, and we'll coach people as much as we can (although we do expect people to do a lot of self-education, though we're always willing to answer questions).

Check out dw_dev, dw_dev_training, the Wiki, especially the Development and Getting Started categories, Bugzilla, and our hosted developer environments so you don't have to install the code. (Which does require a lot more experience than we'd like. Our install process is ... less than stellar.)