1) Have an external Seagate 1TB HD, partitioned into two .5 TBs drives.
2) A Canon Laser printer via USB 2; updated the most recent drivers.
3) Snow Leopard, up to date.
4) iMac, 24", Core 2 Duo, 2.16 GHz, 256 GB HD.
When the printer is connected, the two partitions will not unmount...