Please give the model number of your Studio  (i.e., Studio 1558  or Studio XPS 1640 etc) and your operating system. You should be able to do it but might need to install the audio driver for the jacks to be able to reconfigure to line-in.

It's a 1558

The input jack on that model is both mic and line-in. When you insert a plug into the jack a popup should appear on the screen asking you to identify which type. If you are not getting the popup go to Control Panel/IDT and select to allow popups. If you cannot find that entry then re-install the IDT audio driver or if it is not installed (in which case the audio is using Vista or 7's native HD driver) then install it.

Cheers Jim