Can I remove an older version of Linux (Xandros) and replace it with a hard disk install of Knoppix without losing all the data on my hard disk?

For some reason the Xandros desktop will no longer load and everytime I try to re configure X it kicks me back out. So I want to replace it with Knoppix but I use the computer as a server (at home) so is full of all my music and photo's etc which I don't want to lose and don't have the time to try to back it all up onto CD or another disk.

Any help would be appreciated!

(By the way I am totally new to Linux)