This message will appear at various times, whether or not Spin Doctor is running. To put an end to it, update to the latest version of Spin Doctor. Then launch Spin Doctor and select “Install Audio Capture Support” from the CD Spin Doctor menu. This updates the kext file (located in the /System/Library/Extensions folder) to a version that is compatible with Snow Leopard.
The kext file itself is required if you want to use CD Spin Doctor’s “Audio Music Capture” option. This allows you to “instantly” start recording whatever audio is currently playing on your Mac.”