find, copy, paste

Okay, I'm losing it. I swear I know how to do this, but I'm just hitting blank walls.

On "Sheet1" Column A has 15 values, which populate a listbox. Column B has different values, which are related to Column A. The user makes a selection in the listbox, and the Column A value gets pasted into "Sheet1" in Cell C2. I want D2 to be the corresponding B value. I thought it would be a simple matter to select C2, look up the value in A, and copy the offset value to D2, but I'm not getting anywhere. Can anyone help?

Thanks in advance.