i managed to install a working quatro boot system with xp32, vista64, win7 and Slax (thanks to you).
Now i have to completely reinstall my xp, what is the right way to do it, not to harm the rest of the installation?
Is XP on the same HDD as the controlling boot manager ?
If it's not, you should be able to disconnect the boot drive temporarily, reinstall XP without affecting the boot, then reconnect the boot drive.
If it is, then the reinstall of XP will regress the boot and you'll need to "startup repair" 3 times with the Installation DVD of Vista or W7 (whichever is currently in control - the one marked "system") and then use EasyBCD 2.0 to add the entries which don't get picked up by the repair.