IMac :: 1TB Hard Drive (Seagate ST31000528AQ)/Unable To Shrink/partition?

So I tried to partition my 1TB Seagate main hard drive that's in my iMac, and twice my iMac locked up at the "Shrinking volume" stage. I tried to shrink it down from 1TB to 600GB and it not only did not work, my system locked up (I gave it plenty of time) to the point where I had to forcibly shut it down and a subsequent verification of the disk revealed that it needed to be repaired using Disk Utility after restarting and booting from my OS X installation disk, which worked just fine.

I decided to try again, because the first time, I had not restarted the computer in a while, so I thought I'd "flush out" any temporary files, cache, inactive RAM, and whatever else might have been in the way the first time around. However, this time, the screen simply turned off after 15 or so minutes. Once again, it got stuck at the "Shrinking volume" point and there was also no way to revive it except for a forced shutdown, which, by the way, I did by holding down the power button on the back of the iMac. Same story, I had to restart and repair the disk using my OS X installation disk, which resolved the repair issue.

One more thing. I remember that when I first received my iMac, I was able to partition the drive in order to add a volume for Boot Camp, which I formatted in NTFS right before my Windows 7 installation. All of that worked great and I was actually impressed with how flawless that whole process executed. Eventually, I decided that I no longer needed Windows 7, so I erased the partition and re-consolidated it with the main OS X partition, again, without any problems.

With all of that said, I'm not sure what to try next, but I would really like to create 2 additional volumes. I thought I would try using Disk Utility again, but this time, booting from my OS X installation disk. Then again I didn't want to chance it again, as I have not made any backups yet. I'm in the process of making a backup right now.

So what do you guys think? Should I try to do just that, using Disk Utility after booting into the installation disk? What do you guys think is the reason as to why I can't just resize and partition using Disk Utility after a regular boot-up like I was able to before? What else could I try? Any third-party software titles like I used in Windows? Acronis and Partition Manager come to mind. I'd rather do it in OS X, though.