@overfiend
Welcome! Yes, the A1200 can take a 2.5" HD pretty easily, although you may need a cradle to keep it in the right place (or perhaps some sticky buds, or something)...
Note that unless you've upgraded beyond OS3.1, the machine will not work correctly with a drive that is greater than 4GB - not the easiest of drive size to locate, but really slimline 19mm high drives of this capacity were common in Dell laptops a few years ago - you may be able to salvage one...
