"Want to plug your guitar into your PC? Up until now, you needed any guitar ($100 would do fine) and $200 of add-on devices to do it. The $800 iGuitar USB changes all that." :-/
Pauline, the problem with a fiddle is how to record each string individually, because software has problems recognising simultaneous notes on multiple strings. On a guitar, typically you make this work by adding individual pickups for each string, so the software can work out the note on each string separately. These usually sit in the bridge saddles for each string, and can be easily retro-fitted to replace the all-in-one bridge saddles on acoustic guitars or the individual bridge saddles on electrics. Electrics also have the option of individual coil pickups.
Fiddles ain't so easy. A fiddle bridge holds all four strings, and there isn't an easy way of separating them - even if you put individual pickups under each string, the sound from the other three strings will come through the bridge. On the plus side, you don't usually have more than two strings ringing at once on a fiddle, and software can probably make a reasonable guess at that. So the best solution for a fiddle is probably to use a regular fiddle pickup (of which there are several), record it into a PC normally, and then use some WAV-to-MIDI program to decode it.