From Help > About SolidWorks > License Agreement;
If the Software is permanently installed on the hard disk or other storage device of a computer (other than a network server) and one person uses that computer more than 80% of the time it is in use, then that person may also use the Software on a portable or home computer while the original copy is not in use.
I don't know of any 3D Software that will let you save to a previous version, at least not directly. You could save your '07 stuff out as a parasolid and then run FeatureWorks on it in '05, but that seems like an awful lot of extra work. Lucky for you, as Kelvin pointed out, you can load up '07 on your laptop. Question is, can your laptop handle '07?