I have XP. I installed Win7(7000) 64Bit into another partition, same system disk. Win7 installed without a problem, albeit, is slower than Vista install. 1. After installation, I could not use XP. Machine would boot directly into Win7, no XP option. Boot.ini edit was no help. This has happened twice. 2. Everytime an error occurred, the machine reverted to booting XP as if Win7 did not exist. First time, I was investigating "?" devices (on board sound?) when it crashed with a register dump. Second time, I was running "performance rating" after install. Automatic updates issued a reboot prompt and simultaneously "performance" issued an error. Performance rating has completed successfully before. I have Asus a8n-sli delux mobo with Nforce4 chipset; 4mb memory. This machine has no problems running 32bit XP or 64bit Vista. Bios are current.