Everytime I start time machine, my computer backs up +/- 250MB, then freezes. Tried it with 3 different external drives, all stop at about the same point (they all work fine on other macs). Any suggestions?

Question

     The drives I have are Seagate 1TB GoFlex portable drives (one has UBS 3.0, the other USB 2.0), and a WesternDigital 1TB passport (USB 3.0).  I originally tried to backup with Time Machine using the Seagate USB 3.0, and when that didnt work, Seagate suggested maybe since my operating system is a little older, that I try with a USB 2.0, so they sent me another NEW external hard drive, with the USB 2.0.  Had the same issue.  Frustrated and convinced that Seagate just  sucked, I went and bought the 1TB WesternDigital passport (USB 3.0).  Have the exact same issue again.  Every drive was new, and formatted for mac.  When I started time machine it started to back up my files, but froze after copying give or take 250 MB (usually 252.5MB, to be exact).  I went and tried the drive on several other macs, and none of them presented any problems.  I also tried dragging individual files, but it still freezes on pretty much anything bigger than +/- 100MB.  Disk Utility says that all the drives are fine. Obviously this is a problem with my computer, and not the 3 brand new external drives.  I thought about upgrading to OSX 10.6, but don't know if this'll help or not (plus, I'd really prefer to have all the files backed up on a drive before doing that, just in case).  I dont know what else to do.. called apple, but I'm not about to pay them $50 to have them MAYBE give me a solution (done that twice now for previous unrelated issues, and each time they just told me to take it to a computer repair place.)  Just seeing if anyone out there has a solution before I cave and take it back to the certified computer guys for them to figure it out.. Also, I live in Montana and theres no apple store anywhere close (not suprising), so taking it to an Apple Store is just not an option.
Side note:  Seagate tech support is awesome; they tried everything to solve the problem, and they even bent their rules a little to send me a new drive, even though it wasn't a malfunction issue with their drive.  Really helpful, friendly people, which is much more than I can say for Apple at this point...

Answer 1

this is what you need to do to exclude everything apart from desktop.
on time machine preferences, click on Options
click plus sign, on the new window, click macintosh HD
do a Control + A then deselect users then click okay
go to options again, plus sign, go to users, control +A then deselect your user account
go to options again, plus sign, go to your user account, control + A, deselect desktop
start the back up.