XP 64 bit is only available as OEM software, therefore if you want to use it, you are either going to have to format the hard drive with the 32 bit version on it and install the XP64 or you will have to get another hard drive, put it in, and install XP64 on it.

IMPORTANT TECHINCAL NOTE ABOUT OEM AND DSP SOFTWARE:

OEM and DSP operating system software from Microsoft cannot be installed as an Upgrade, unless the old hard drive has been formatted or you are installing a new formatted hard drive. If you format your existing hard drive in order to install your new operating system, you cannot use the original manufacturer's recovery disk before loading the new operating system. You can load the new operating system without using the original manufacturer's recovery disk. Most or all of the component drivers should be located on the new Windows CD and therefore your recovery disk (if you have one) is not required. CLICK HERE for formatting and partitioning hard drive information.

OEM and DSP non-operating system software (such as Microsoft Office, Works Suite, WordPerfect, etc.) also cannot be installed over a previous version as an Upgrade. Installation of newer versions of OEM and DSP software on hard drives where older versions were previously installed will add updated system .dll's and .ocx's which will render the older version inoperable. We recommend that you back-up your old files on some reliable media such as CD-R, ZIP disk, or floppy disks and then UN-INSTALL your previous software version before installing the newer OEM or DSP version. You may also purchase a retail box upgrade version (if available) which will install over a previous older version and transfer your older files into the newer version. Most manufacturers allow upgrades only from versions that are 2 versions old.