There are two groups of API functions working with the Registry:

Registry Functions
Shell Registry Handling Functions

Some names of API functions:
GetPrivateProfileSectionNames
GetPrivateProfileString
GetProfileString
RegCloseKey
RegEnumKey
RegEnumValue
RegOpenKeyEx
RegQueryValueEx
RegSaveKey
SHEnumKeyEx
SHRegCloseUSKey
SHRegEnumUSKey
SHRegOpenUSKey
WritePrivateProfileSection
WritePrivateProfileString

Take a look at the Shell objects as well -- methods RegRead, RegWrite, RegDelete etc. -- very often is easier to use than API functions.

FoxPro examples with API functions:

Testing MS Internet Explorer version installed
http://www.news2news.com/vfp/?example=142

Saving specified registry key to a file (subkeys and values included)
http://www.news2news.com/vfp/?example=135

Saving HKEY_LOCAL_MACHINE\\Software\\ODBC Registry Entries to an XML file
http://www.news2news.com/vfp/?example=379

Reading VFP 6.0 options from the Registry
http://www.news2news.com/vfp/?example=131