I have to retract a statemrnt I made a while back, that FirstDefense-ISR will not! run on 64-bit systems. Having installed Xp Professional 64-bit yesterday, initially I was confronted with * Disk write error* when I installed FD-ISR and tried to boot-back to my Primary snapshot which was Vista Ultimate. Clearly something went wrong here, and the entire partition was deleted somehow Today I reformatted my drive and did a clean installation of XP Pro 64-bit Only, FD-ISR installed without a glitch,and created secondary, and Backup Baseline snapshot. It seams to be running just fine, However I am hesitant to create an Empty snapshot to install Vista,as its taken a few hours to setup my system again. This may not be the case for Everyone, but I do Advise *CAUTION* If installing Vista or Vice Versa on 64-bit systems with FirstDefense-ISR and then choosing to install the Secondary OS. Hope this little bit of Information will Prevent Pain-staking situations like what I had, for Others.