Hypersmurf said:But "You can't take a 5-foot step if your movement is hampered" (3.5PHB p304). If you can normally take a move action to move 30 feet, and while prone can only take a move action to move 5 feet, is your movement not hampered (thus disallowing a 5' step)?
It depends:
"Take 5-Foot Step
You can move 5 feet in any round when you don’t perform any other kind of movement. Taking this 5-foot step never provokes an attack of opportunity. You can’t take more than one 5-foot step in a round, and you can’t take a 5-foot step in the same round when you move any distance.
You can take a 5-foot step before, during, or after your other actions in the round.
You can only take a 5-foot-step if your movement isn’t hampered by difficult terrain or darkness. Any creature with a speed of 5 feet or less can’t take a 5-foot step, since moving even 5 feet requires a move action for such a slow creature.
You may not take a 5-foot step using a form of movement for which you do not have a listed speed. "
Where does it state that being prone results in difficult terrain (or darkness)?
The creature also still has his speed while prone. Whether he can use that speed or not to move could be considered irrelevant to whether he has that speed.
So, what stops: 5 foot step, stand up, use standard action?
Note: I do not have my PHB here, but do not see anything in the SRD.