Marie - P
The 10 gig 30 gig split will work. You can install Linux to a single partition, but I would recommend installing a swap partition, the OS to another partition, and your home to a separate partition. Take a look at your existing Suse system to see what tools come with Suse for partitioning and formating. The reason for this setup, is to allow you to re-install the linux system, without loosing your /home. Home is where your user data goes. If you don't separate them, you woudl have to backup and restore your user data. That can be a significant task. There are lots of threads on partitioning, and the "best" way to do it. There are as many ways as there are opinions.
Formatting does not get rid of partitions. You need to use fdisk, or partition magic to do that. There are also linux programs to delete partitions. Fdisk will create or delete a partition.
When you install linux, you should get an option to install a boot loader, either Lilo or Grub. Lilo is a little easier for the first time dual boot system. Both will work. You will need one or the other in order to boot either XP or Linux. This is not automatic as you suggest.