it really works on xp, ho/pos can't be held, you cant pick a ho/po, you cant hold a lower fret to play a higher one, there's no support for two key chord conversion.
this is the detailed description of gameplay :p
To play multiplayer... create a server/connect a server, choose a song, make sure your friend has the exact same folder(doesn't have to be in the same location, just the same folder name and files), then if the game doesn't auto start, you pick the song he chose, after that it's pure shredding xD.
Needs to be ported/upgraded but since it works over the internet, it ownz
