Hello greglives Welcome to the Seven Forums!
The most often recommended first move besides downloading a fresh copy of SP1 is the advice to run the System File Checker and Disk Check tools in order to fix any minor errors on the main volume or replace any system files found corrupt or missing.
Another item of interest is a blog found at the MS TecNet forums you will want to look over on this type of SP install problem with several other MS references being pointed to. General guidance before installing Service Pack 1 for Windows 7 and Windows 2008 R2 - The Windows Servicing Guy - Site Home - TechNet Blogs
To start the SFC tool simply go to the Start>Run command line or open up a command prompt to type in "sfc/ scannow" and press the enter/return key to get that going. You may want to have the Windows 7 dvd in the drive if you have one onhand in case the SFC prompts for it.
For seeing the Disk Check tool scheduled for the next startup or to watch it run live when booted from the 7 dvd or repair cd if you saw one created holding the repair tools you have 3 ways to get that one going two in Windows. 1) open an elevated command prompt by right clicking on the command prompt icon found in Start>All Programs>Accessories and selecting the run as admin option.
That will see all necessary permissions are granted. Then you simply type "chkdsk /r" and press enter. R is the automatic Repair switch added at the end.
2)In Windows Explorer or Computer simply right on the drive's own icon and then open up the Tools tab. Under the first Error checking simply click on the Check now button to see the tool scheduled for the next start up. Note the Automatic repair box is already checked off for you.
3)The live boot option simply requires a trip into the repair tools while booted live from a repair cd if not the 7 media used to install Windows and select the command prompt option there. Simply type in "chkdsk c: /f" with F for fix being the switch used at the end there and press enter to start it off. Once it finishes you simply restart the system and boot into Windows normally again.