i) Backup /home
You should do this before any major surgery, even if you know that you don't need to. If you know that you need a backup, you probably should make 2...
you have a separate partition for /home, most installs will 'do the right thing' if you ask them to
. Only trouble is that the descriptions in the installer aren't always totally clear, so it may not be as clear to you as it should be which options to select to get this behaviour.
Also I had to reinstall my windows XP... Can I fix this by using the Suse install cd?? Once again I donīt want to lose the data if possible.
It depends what you have done so far. In general, windows of any version doesn't do anything to assist co-operation with other OSs (ain't that a surprise!) so what you have to do is to let windows install as if were the only OS that was going to boot and then sort out the problems that windows has created with an open source tool (either Grub/Lilo or by a re-install).
But it is necessary that you have not let windows use any of the disk space where you have your data from other OSs. If you have made the mistake of allowing windows to use the whole disk then data recovery is somewhere between difficult and impossible.
Also note that there is some abiguity in 'the data...'. Yeah, its all data, but in /home/username you will not only have the explicit user data, but you'll also have setup files for various applications, usually hiding somewhere under a dot file (a directory tree structure 'hidden' from normal vision by being headed by a directory whose name starts with a dot). That is likely to be absolutely fine if you are installing the same version of the application; if you are installing different (later?) versions of the applications it is likely that some of the configuration directives will not be understood. This may or not cause problems.
The solution is usually pretty simple though; if, post-install, an app is misbehaving, rename the tree containing the config for that app.