Why there are extended...
You might first use a linux live-cd to open a terminal and with root privileges type the command "fdisk -l".
This will read the partition tables and perhaps show you that if Windows is installed, there is a hidden Windows rescue partition as well as the Windows OS partition. Two of the primary partition will have been used.
If this is the case, when you install linux, use the openSUSE partitioning tool to create an extended partition. You may have swap, root, and home as logical partitions as well as whatever others you need within the extended partition.
You will have to create the partition yourself, but it is not difficult. Remember that you can perform all the act of installation including partitioning without making any changes before a warning that the installation process is about to begin. You can explore and fumble without doing any harm.
If you have Vista and want to shrink its partition, do so with the Vista partitioning tool or as a consequence, Vista will not boot.