The finder listing on a 10.5 or 10.6 is really slow when you browse folders, move files, detele etc. - you see the turning wheel all over the place...
Solution - the hard way
The solutions below works, but somtimes you need to get a fresh start.
Make a running boobeable copy of your system on an external disk with superduper.
Once you have found that the disk works you have two options: