Hi John & Happy New Year!
The short answer is yes, but we could be more exact if you could review exactly how the drives are set up, or upload a screenshot of the Disk Management dialog box (Photobucket or ImageShack) and post it back here.
You can drag n drop folders or files from one volume to another. If it is to a separate drive, the folders/files will be copied and you could then delete the same on the full drive. Or you could store rarely used files on the second volume. You could also move your libraries to the second volume but that's slightly more involved.
If this is a single HDD, with 2 or more volumes (check in disk management) you can simply with Win-7 expand the full volume, adding space from the empty volume to the full one and not have to move any files. That's done in Disk Management, right clicking on the full volume, choosing Extend Volume, follow the prompts.
If you can post the disk management screenshot, makes it much easier to understand your setup and give you the best options.