Depends on what games you are talking about.
If the games are Steam games then it's really easy to backup.
Oh the old drive where your games are installed, rename the folder, then download and install the Steam client and login after you done that, exit the client and copy and paste all your game folders from the old Steam folder into the new Steam folder be it common, name, whatever folder it has to be.
Start up Steam and all the games will be installed again.
Remember to back up the save folders that are elsewhere in the old OS or you lose everything.
You shouldn't have any problems when starting the games, some might want to update and download a few files, but I only ever had that once or twice after many installations.
CD installed games will still work but I recommend you reinstall them again.