ya . sort of . . after u format xp , u need not do the vista repair . vista controls the multiboot , so u format xp , u just loose xp , vista will be fine . xp will still be in the boot menu , but if u choose it , some error comes or ur system restarts . but vista will be in the boot menu and will be fine .
the prob is abt linux , u remove xp and install linux then chances are that u might loose vista . u have to use the vista boot dvd and repair vista boot loader. BUT , during this , chato cheeta is suggesting that after u repair vista boot loader , ur linux may not be detected by vista boot loader .and hence GRUB , it might detect vista or vice versa . if u got good luck , it'll be vice versa .
so its damn simple if u just want to remove xp , but not that simple if u want linux . ( it may be if grub or vista boot loader recognizes the other os ).