Which Mac is returning this fanciful arithmetic? The likelihood of your shifting a nominal 1.8GB file from the SE to the iBook is slight, even if you had one on the SE's hard drive. One of the Macs must still have had its shoes on. This kind of orders-of-magnitude miscalculation of hard drive space frequently comes from failing/failed drives (or their 'drivers'), and it may argue that one of them needs its driver re-installed.
de