Regarding the right side, there is a series of 3-4 plastic snap in locks on that side along the optical drive, holding the case down in lieu of screws. It takes serious pressure to remove the snapped in pieces (just lift straight up). You should also make sure to line them up when you put the casing back on. Another picture might help show that portion better
Installing MacBook Core Duo Upper Case
Regarding the right side, there is a series of 3-4 plastic snap in locks on that side along the optical drive, holding the case down in lieu of screws. It takes serious pressure to remove the snapped in pieces (just lift straight up). You should also make sure to line them up when you put the casing back on. Another picture might help show that portion better