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It really depends how much data there are to transfer. Large amounts of music and films/photographs might warrant a converter to enable you to slave the XP hard disk to the laptop via USB. Small amounts can be transferred using memory sticks or small external disks.

From XP you need to copy everything in C:\Documents and Settings>{yourusername}>Documents then, Music, Pictures, Videos Desktop, Contacts, Favourites and any loose folders you might have. In Vista those data live in C:\Users then the same folder names as before. If you use Outlook or similar for e-mail handling, post back for details of how to move those data files.