If there is no setup to take advantage of, then simply use a USB Flash Storage drive with 4GB+ of free space to transfer Diary Keeper to the other PC. Simply double click the executable file on the new PC to run it. The software will run in shareware mode until you enter the registration number. Add that number and continue using the applications.
You might encounter compatibility issues, therefore right click the executable file and choose Properties > Compatibility. Select Windows XP from the list and run the software.