ASP.NET Custom Control, Two Grids.. Need some advice

I need some advice designing a custom control which uses two grids and an Add and Remove button in between.

The Add button takes the selected item from left and add it to the right and then it removes it from the left.

The Remove button does the vice versa.

To have a fluid experience, I understand that Javascript will probably have to be involved.

Currently I'm creating a control inheriting CompositeControl with two grids and two sources. I could use a UpdatePanel so I don't have to do do a full post back on Add/Remove.

Any suggestions on the best way to approach this?