[Vikesrock]

EDIT: Or apparently you can skip my whole post and use one VI to do the conversion for you.

To find the angle and magnitude of the joystick motion you are going to need to do some math with the joystick inputs.

I could just post the formulas here, but I think you will learn a lot more if you understand them so I'll post the idea and let you do the digging.

The joystick VIs allow you to access the Cartesian coordinates of the joystick (X,Y) where X is a left-right coordinate and Y is an Up-Down or Away-Towards coordinate. You want the joystick values in Polar coordinates (Theta, R) where Theta is an angle and R is a magnitude from the origin. You should be able to find more information on the coordinate systems and the formulas for conversion with some digging (if you can't find it try asking a math teacher, if you've still got nothing feel free to come back here).

One thing to be careful of is the 0 reference for the angle Theta. I'm not sure what range of values and reference the Holonomic drive VI takes but finding formulas for theta will give you either a 360 degree or 2*pi scale with theta=0 pointing in the direction of the positive X-axis.