Can't create Windows partition!

Hello,

I'm trying to create a new partition to install Windows 7 on, but I am unable to do so.

At first I tried to do this with Boot Camp Assistant, but it didn't work.

Then I tried to create a FAT partition with Disk Utility, which didn't work either.

So I verified and repaired the disk, tried to create the partition again, yet it still didn't work.

I verified and repaired the disk and tried to create the partition while running the OS, in Safe Mode and from the Mac OSX Install DVD.

Neither of them worked.

I noticed while running the OS, the info of the HD said the capacity is 749.81 GB, while checking that from the Mac OSX Install DVD it only says about 700 GB (I mentioned 698.6 GB).

Strange..

It might also be important to mention that I recently (2 days ago) I installed a new HD: Western Digital Scorpio Black 750 GB, and today I swapped my 2x 2GB RAM for 2x 4GB RAM (Samsung).

On my previous HD, the Fujitsu 250GB, this proces was no problem at all. I installed W7 on that drive just a week ago.

I made a clone of the Fujitsu HD and "back-upped" it to my new WD HD. The W7 partition on the Fujitsu HD was 50GB, which is the difference in capacity mentioned above. I'm not sure if there's a link here..

I've got a MacBook Pro from mid 2009.

I'm not sure what to do next... I'm stuck!

Any help is greatly appreciated!