You could use a small, damp cloth to lightly clean the keyboard. Clean each key carefully. Don't make broad, sweeping movements across the board or you're likely to break off a keycap.
Underneath, you could try compressed air.
Don't know what to tell you about the space key. Mine squeeks every time I press it with my right thumb. Very annoying.
have a search around the 'net. you should be able to take each key off your keyboard to clean it out. I did when I had my TiBook. just make sure you find some instructions that show exactly how to do it, or you could end up breaking the keys.