or create partition and boot from vista disk....it will ask where to install...just dont say the same partition as xp...it will replace bootloader and you will get the choice when booting...
tis how i did my mce2005/vista32 dual boot
intel i7 3770k @4.4, ASRock Z77 Extreme 4, 16GB Corsiar Vengance 1600 ram, ATI 5850 BE, Antec 1 Case, Antec 1 550W PSU, emu0404, 120gb agility3 ssd OS, 2x60gbvertex2raid0 Games, 3 TB total sata2 Data. win7 x64.