User created directory

Hello,
i've added a custom page to my (mui) script where the user can select in which directory some data from a zip file should be unpacked.

I want to add a registry entry for the choosen directory. This entry will be used from my programm. Also i want that the uninstaller deletes this directory and the registry entry.

How can i do that? Can anybody show me some code example?

Just read the value from the ini field that contains the selected directory and write it to the registry.
EXAMPLE:

ReadINIStr $0 '$PLUGINSDIR\custom.ini' 'Field #' 'State'

WriteRegStr HKCU 'software\My application' 'InstallDir' '$0'