My PC has a single drive, with currently two partitions, Win7 x86 and Data, plus two other (OEM and system-reserved)

I want to create a third partition to install Win7 x64, but the installer didn't like the fact that partitions were dynamic. I don't know if there's a way to recreate basic partitions, and make my data partition dynamic, since I read that I can have 4 basic partitions? I have GParted liveCD, but before I'd prefer to ask here what is the best partitionning option.