You can create a new album and copy photos over to it from another album or your Camera Roll.
Albums > Edit > New Album > pick an album (or Camera Roll or Photo Stream) and pick photos from it for the new album.
No synching or computer needed. All done on iPad.
But I've not tried moving photos into an existing album. Not sure you can do that.
(With iPad 1 on iOS 5, Camera Roll is now called Saved Photos, presumably because iPad 1 has no camera.)