My N8's fm transmitter won't even get picked up in the car when I'm sat inside it yet I have a cheap'o ebay special FM transmitter which can broadcast all around the house and in the garden... Great for partys!
I also would like to boost the signal of the FM transmitter. I don't belive that the chip inside the n8 is capable of breaking the broadcasting law since you would need a huge aerial (like you see at a taxi office) for it go more than a few metres.
On another note, I would also like to expand the bandwidth so it can broadcast on 87.10 up to 108.00 (the standard bandwidth of a UK radio) due to the fact that 108.00 is normally free but most other frequencys have been taken by other radio stations which interfears with the weak signal of the n8.
Found this for the n900 http://maemo.org/downloads/product/Maemo5/fm-boost/
is there anyway it could be used to program a s^3 app or TweakS app.... might have to see if CoderuS is free...