SuSE will format the partition to whatever it needs. However, I'd strongly suggest having more than one partition set aside for Linux. I'm not familiar with SuSE's installation process, but it may give you the option to automatically divide up the available space. Do that, if possible. At any rate, it will probably allow you to repartition the available space prior to installing, so you don't need to use Partition Magic for that.
I don't know anything about BootMagic, but SuSE will certainly give you the ability to dual-boot with Windows; even if it does not boot into Windows by default, it's relatively easy to configure that behavior after you've installed.