If your recovery disk is anything like the unbranded SP1 OEM recovery disk I originally bought once you choose the install now option by simply ignoring the press R to repair seen when the installer starts you look for the option to repair the current installation.
What does a repair install do? Without seeing the original Windows and other MS created directories deleted and replaced with new ones like you see with a full reinstall those are preserved along with all the programs you have on now.
The repair install replaces the main system files as well as correcting any boot problems with new entries in the master boot record as well as restoring the registry if finding a hive missing there by looking at the backups made already by Windows. Some items like sound and video drivers and even software for keyboard/mice may have to be reinstalled while the rest remains intact.