you can get an ic which is an fm radio receiver similar to a tda 7000, it has autoscan tuning, one of these is quick and easy.
Probably aquiring a cheap autoscan fm radio is a good place to start, you could use the handshake signals on the serial port to control the scan/reset, and feed the audio out back to the line in on the soundcard.
Altogether a very minimal circuit, if you use a lappy then you could use a usb to serial adaptor.
You can also get usb to relay modules, this would also work well and the software is allready done.
If you want direct control and display of the frequency and volume etc then your into a more complex project, still doable.