The PC I added suse 11 to had Windows installed with 3 partitions. After that it also has a Debian install.
The suse 11 installer found my Windows install also my Debian install, but it thought that each of the 3 partitions of Windows was a separate OS, even though there are no OS files on them. I think that’s a bug b/c no other installer ever made that mistake.
It was also fairly odd that when it went into the auto configuration section (IIRC) the screen layout/color changed and it seemed to be a new app. IIRC the suse 10 installer was a bit smoother here.
Once up and running, I had a blank screen, due to Nvidia card. Would be nice if at least the installer detected that and set me up with Vesa so I could login, but anyway no other Linux installer does that, so I can’t complain. 
Using the ymp from NVIDIA - openSUSE was very nice and very easy BUT when I rebooted, there were 2 new options in Grub. I understand that the kernel was rebuilt but there is no reason to add two new options in Grub–not to mention that the default was set to the wrong one, so it booted into a kernel that couldn’t load the Nvidia drivers. I rebooted and figured out which one to use and now all is well.
The other thing I wanted to note is that I did the partioning manually but the installer identified all 3 windows partions and offered to mount them automatically for me. That was VERY nice and no other installed ever did that.
I haven’t really installed SO many Linuxes as a dual boot–most of those I installed were single OS.