If you have a separate /home partition, 11.1 will find 10.2 and suggest it overwrites just / .
Depending on how many KDE4 applications you intend to use, you may have to transfer some hidden files in your /home partition to the relevant .kde4 folder.
If you do not have a separate /home partition, you may wish to consider backing up /home and letting 11.1 create one for you which it will do if you use expert mode to indicate which partitions to overwrite in doing this.
Before you leave expert mode, make sure that 11.1 has set a mount point for XP.
None of this should have the slightest impact on XP but I would still back up XP before starting.
In this video, (it’s 11.2 but no matter) when you get to custom partitioning, all your partitions will already be there, all you have to do is expand the tree on the left and select whichever are / and /home
With each go to edit and format as ext3, set the mount point for each as appropriate, windows and swap will not need touching.
make sure at the summary in ‘Booting’ it is set like this http://files.myopera.com/carl4926/albums/671478/19.png