The process of importing GH songs into FoF is quite a long process and it is advisable for you to simply download them instead of ripping; you can find them on the Getting Started wiki page.
1. Download the OGG Encoder and unzip it. Put the oggenc2.exe into the main folder of your Frets on Fire installation and rename it to oggenc.exe. Also make sure you have at least 1 GB of free space for the songs folder to fill up.
2. Run Frets on Fire and pick Song Editor > Import Guitar Hero(tm) Songs.
3. Enter the path to your CD drive with the GH disc inserted.
4. Wait. It takes at least several hours.
The importer does not work (yet) with the GH Encore - Rock The 80's.