Originally Posted by Trickster
Posilo, what was your solution?
Oh, sorry for being so secretive: I also followed rev918's suggestion and it worked. As an absolute beginner with Linux I was just unsure how to deal with the command lines... but figured it out myself.
(By the way, if you want to hear something funny(?!), after doing that, I managed to format the whole HD of my laptop with GParted while all I meant to do was resize the newly created partitions and leave WinXP as a secondary option... But that's another story, and now I have just Xubuntu and I'm happy with it. )