I agree with Dave - it's a worthwhile exercise to think through the whole of this problem with the particulars of your drive system. This is the first year our team has attempted a swerve/crab system so I'll say a little about how we approached it. But first I'd like to put in a plug for not using standard kit joysticks.
We have had some success in using the Logitech Dual Action Game Controller (~$20 from Target) to control the crab/swerve drive system we developed this year. The Logitech device gives you a pair of thumbsticks along with numerous buttons, and our drivers seem to prefer it to traditional full-size joysticks. Being hand-held you can stand slightly away from the team station and also stand at full height which helps a little in seeing the action on the field.
The original idea was to use the control sense of video games such as Halo, where the left stick controls forward/reverse left/right movement (translation) and the right stick controls rotation
http://halo.wikia.com/wiki/Halo_Controls
We changed that a bit during development, and ended up with a control model where the left stick controls speed and the right stick controls the various forms of steering.