Do you have two hard disks?
If you do just install SuSE on to the second Hard disk.
If you don't mind losing your files
you can do it in the installation.
(this might not be 100% accurate as I have Mandrake, but it should be roughly the same.)
If your machine boots from cd (make sure you enable this in the BIOS settings)
(if not use the boot disk to start installation)
(you will have to re-install Windows)
just put in the installation cd and it should find it and start the setup. The should be an option to format the hard disk into bits. you should (depending on the size of your hard disk)
have a FAT32 partion (for windows (but LInux can read and write to it))
Have a linux partion
Have a swap file partion.
Then finish the setup and you should be done if your system is normal.
If you have two hard disk it's much easier all you need to do is put a linux parion and a swap file partion on that disk and all should be well.
I am a Mandrake user, this process may be different with SuSE (if anyone else has a more accurate answer for SuSE please post it)
I am a newbie if I am wrong please post a correction.