Even though I had a choice of creating a SP1 DVD using the .iso file, I choose to use the windows6.1-KB976932-X86.exe file download to install SP1.
The install took about all of 15 minutes, although the installation warns that it might take an hour or more and your computer may need to restart sever times during installation.
Scroll down to view the slde show of Service Pack 1 installation.
The progress bar is not entirely accurate as it bounces backwards and forward until it finally reaches 100% and stays there for a period of time.
Note: The display may go black for a significant period of time, (if your Power Plan's ‘Turn off display’ settings is set to the default of 10 minutes) during which disk activity is your only indicator that something is going on. I suggest you set the plan's display and sleep settings to a least 1 hour.