Check to see if your anti-virus is active during the registration. If it is McAfee's VirusScan 8.0i, then you will need to disable the "Buffer Overflow" function in the application. In addition to this, right click on My Computer and select Properties. Then click on the 'Advanced' tab and under 'Performance' click on the 'Settings' button.
Click on the 'Data Execution Prevention' tab. Select the 'Turn on DEP for all programs and services except those I select: radio button and click on 'Add'. Navigate to "C:\Program Files\ Adobe\Adobe Photoshop CS2\Photoshop. exe" and click Open. Now click on Apply and then Ok. Restart the computer and try the registration process again.