I have a 20Gb Seagate, I set it as a slave (40Gb Maxtor being master). When I open "My Computer" it tells me that my seagate still have 5.75Gb of free space but when I browse it I only shows "My Documents" folder and "mydocuments.000" file (I moved My Documents' path to the Seagate drive).what happened?. and what should I do?:(

Did you format the Seagate drive before using ? I ran into this problem when I installed a 160 Gig Seagate but after formatting the drive all went well.
I hope you backed up all your documents to CD from My Documents before moving to the Seagate HD.
You might go to
http://www.seagate.com/contact/index.html
Under Technical Support, there is a link you can use for e-mail and get Technical Support.