QUOTE(Reaper527 @ Oct 23 2007, 07:15 PM)
as far as moving from medium to hard, try playing heart shaped box. that was the first song i 5 starred on hard, i personally found that song pretty easy. also, you can try going into practice mode and slowing the songs down. this will give you the ability to play with the extra notes, but at the same speed that you did on medium. worst case scenario, just pick a song in the first tier, and play it 5 or 6 times. you'll notice that you get further and further each time you play. also, try saving your star power for the solo section. you won't get big scores that way, but it will keep you alive through that section while you get better at the game.
also, hammer ons and pull offs are you friends. check the in game tutorial for more info (you'll get an achievement for checking the tutorial anyways).
This is how I learned the curve from medium to hard/expert. Also, you can try to play medium with your index finger on red and pinky on orange rather than index on green and pinky on blue. It helps getting you used to holding your hands in that position for hard and expert.