I'm running a W7 Ultimate OEM. Your right I installed it on a clean hard drive and have had not problems. 32 bit & 64 bit are on the same disk. It installs a 32 bit OS, later after if you want you can put the disk back in and upgrade to 64 bit. I'm staying with the 32 bit for a while. I see no reason to go 64 bit right now. You can always upgrade, but to down size you got to reformat and start over.