AFAIK there are no known hardware issues with connecting a 2.5" IDE drive to an A1200, however there are software issues regarding being able to use all the space available on the disk. AFAIK these are all possible to overcome with relative ease, but I've never had the problem as I'm using an 880MB disk. Other people here should be able to clue you in on that (I don't think it necessarily means upgrading OS, but not sure).
