@BoingBoss: I agree, all those people answering here must be drunken.
@DeltaWolf:
Whenever you insert a disk into one of the drive, an Icon must appear on the Workbench desktop. If it does not appear, your disk drives are faulty, they don't recognise disk changes.
Does it really say there is no disk in the drive, or does it actually say there is no *DOS* disk in the drive ?
If the latter than it tells you, the disk is not formatted in AmigaDOS format and it cannot read from nor write to it.
In tsgui you can enable the "format during write" option, then it will format the disk on the fly. If you want to use one of the other programs, you first have to format the disk before you can use it (or check if they have a format option either).
Bye,
Thomas