Go for XP, as Vista really sucks.

For security Vista is much better but I don't think you will be attacked by a pro hacker but maybe you have some secret documents of the Area 51 hidden in your laptop...LOL

Install XP with the latest Service Pack 3, it is much faster and more stable than Vista even with its SP1.

With Vista you light also have some compatibility issues with peripherals drivers and some softwares.

My advice stay with XP SP3.

Good luck