my old soundblaster way great for this! never thought I'd be reminiscing about the SBlive! Ofcourse not the right quality but it had a 'record what you hear' function which was handy, sometimes i used it as well as my motu just for this purpose. Another option may be to import the movie into a DAW eg Cubase and record what you hear using TapeIT. Or if your on windows use 'Windows Movie Maker' where you can split the audio from the video.
-I'm sure you could do the job with whats lying around.
Someone also once told me here that KVR was my friend.. I'm not sure what they meant by that but you may want to search through that
KVR: Virtual Instruments, Virtual Effects, VST Plugins, Audio Units (AU), DirectX (DX), Universal Binary Compatibility - Audio Plugin News, Reviews and Community