I was searching the space marines section at a local warhammer shop when I saw a miniature called the space marine commander, I looked for it in my index but his rules weren't in it. What are the rules for a space marine commander? Do they follow the same rules as the captain? Please let me know so I can decide whether to get him or not.
Was this Space Marine Commander the miniature you saw?
If so, at least according to the description on the website, it appears you'd be treating this as a Captain for rules purposes:
Space Marine Commander
A Captain leads each of the ten Companies of a Space Marine Chapter. They are second in experience only to the Chapter Master and each is a warrior so deadly that he will rarely meet his match. Each Captain is an inspirational and determined leader, able to coordinate the Space Marines under his command whatever the opposition.