Move Silently (Dex; Armor Check Penalty)
Your Move Silently check is opposed by the Listen check of anyone who might hear you. You can move up to one-half your normal speed at no penalty. When moving at a speed greater than one-half but less than your full speed, you take a -5 penalty. It's practically impossible (-20 penalty) to move silently while running or charging.
Noisy surfaces, such as bogs or undergrowth, are tough to move silently across. When you try to sneak across such a surface, you take a penalty on your Move Silently check as indicated below.
Action:None. A Move Silently check is included in your movement or other activity, so it is part of another action.
Special: The master of a cat familiar gains a +3 bonus on Move Silently checks.
A halfling has a +2 racial bonus on Move Silently checks.
If you have the Stealthy feat, you get a +2 bonus on Move Silently checks.
Source: SRD 3.5 Combined Skills