IMC, from my house rules:
TUMBLE (Dex; Trained Only; Armor Check Penalty)
You can dive, roll, somersault, flip, and so on. You can’t use this skill if your speed has been reduced by armor, excess equipment, or loot (see Player’s Handbook, Table 9-2: Carrying Loads, page 142)†.
Check: Tumble performs exactly as the skill outlined in the Player’s Handbook, page 75, except as noted herein. When tumbling, you suffer attacks of opportunity but gain an AC modifier equal to the difference between your Tumble skill check and the difficulty class plus 1. The DCs for tumbling remain the same (DC 15 for tumbling past opponents; DC 25 for tumbling through opponents). Failure means that you come to a stumbling halt in the first threatened square you enter; you do not incur an AC penalty.
Tumbling consumes the entire movement action whether you succeed or fail. You cannot tumble 10 feet and then move 10 feet as part of the same movement action. You can, however, tumble up to 20 feet and then move normally as your move equivalent action.
Retry: You can attempt to tumble as part of a movement once per round.
Special: For other benefits of tumbling, see the entry in the Player’s Handbook.
Cheers,
/ds