Space constraints

This work fine :

http://www.id-design.com/software/whatsize

In the finder if you hit Command-F for Find - and the Click where is says Kind and choose other - then add Size to your list of criteria - you can then search for all files greater than 1 GB for example. Not sure if it will show hidden system files though unless you add Invisible items to your search criteria.

Do you use a program such as Photoshop that creates scratch files?

Do you have backup software running that uses the same drive as the source and target?

One problem with the Find result window is that it does not show the size of the files and I cannot seem to change the view parameters.

You could use the terminal and a command such as: find / -size 1G to find all files at least 1GB in size - may need to use: sudo find / -size 1G and enter your admin password to scan certain areas.