If when attempting to upgrade from Windows Vista to Windows 7 your installation hangs at 62% this could be due to the iphlpsvc service and Microsoft offers the following fix:

1. Reboot the computer; this will cause a rollback to Windows Vista.
2. Click Start, and right-click Computer.
3. Click Properties, and then click Advanced System Settings.
4. Click Environment Variables.
5. Under System Variables, click New, and then press ENTER
6. Type in the following variable information:
   Variable Name: MIG_UPGRADE_IGNORE_PLUGINS 
   Variable value: IphlpsvcMigPlugin.dll
7. Then Restart Setup.

Note This workaround only applies to the iphlpsvc service hangs

Microsoft Support article