HD's, esp Western Digital's, had experience failing more then others so I would invest in a good AIT-3 tape drive. I'm sure there's drives compatible with SuSE esp the newer versions. I'd try reading up on the GFS method (grandfather, father, son) of backup sceduling so you can optomize it based on your setup/use.
I would also look at making dated tar archives of your backups that you would store on the SuSE box (again you need to decide which you want to store locally eg. most recient or oldest or whatever) that way you have them accessable locally and you can store the tapes offsite (highly suggested). Based on your budget restrictions/how much time your willing to spend, see where you want to go with it.
You could also look at getting a dvd burner for the XP box and burning the most critical images/clients straight to DVD. It would probably be the cheapest but not the most logical as DVD's are just as fragile as any other CD media. Again you have tons of options, these are just a few off the top of my head.
Matt
piet