If you have WinXP, then the Audio and Graphics folders for the RTP are located here by default:
C:\Program Files\Common Files\Enterbrain\RGSS\Standard
Not sure if it's the same if you have Vista or Win7.
If you still can't find it, then do a search for 137-BunnyGirl01 on your computer.
Go to Start > Search > Look In: Local Disk > type in 137-BunnyGirl01 > Search > wait.
Once you find 137-BunnyGirl01, right click on it and choose Open Containing Folder.