I’m using openSuSE 10.3 at the moment and loving it! I’d upgrade to 11.0 if I could be bothered but I’m sure I’ll get round to that soon enough.
The partition manager that comes with openSuSE is able to do what you want, and comes with a boot manager (either LILO or GRUB, GRUB is default) to allow you to select between Windows and SuSE. I’d just recommend that you’re careful when you install it since it’s pretty easy to get the partitioning wrong and lose some data. Perhaps as geno said you could try it on a separate hard disk or better still a different computer.
Hope you enjoy Linux, I definitely was happy to switch over. Just bear in mind that you will have a lot to get used to and it can be frustrating occasionally. It’s not Windows and it’s not trying to be, so lots of things will be in different places or done in a different way altogether. Also, perhaps you’ll end up like me with a Windows partition still alongside the Linux one for those occasional applications you can’t live without (in my case it’s games and while they can often be made to work in Linux there are simply cases where it’s not possible, at least for the moment). I spend the majority of my time in Linux though, and I’m looking into running a VMware install of Windows within Linux for certain (non-game) applications.
Anyways, have fun!