Sil said:
1)Whirlwind substitutes for a full round action does it not?
No. Whirlwind Attack, like Flurry of Blows, is an option you may elect to employ whenever you take the Full Attack action. Accordingly, it follows all the rules about Full Attacks (including a 5' step allowed in before, after, or between any two attacks).
2)Is not the use of cleave/TWF explicitly banned when using whirlwind in place of your full round action?
Cleave / TWF are not generically banned when you use the Full Attack action. It is, however, specifically banned "while using Whirlwind Attack," per the text of the feat. However, if the logic of the "natural weapons after a flurry" group holds, then WWA ends as soon as you make your last WWA, and you may then employ any additional attacks you desire.
For example, let's assume there are three potential targets for you to attack. Under my reading, once you attack each of them, your full attack and your WWA are finished.
Under the others' reading, once you attack each of them, your WWA is finished,
but not your full attack. Therefore, if I kill the last guy I attack, I may now Cleave, because the limitations of WWA no longer apply.
3)How do you use your full round action, and still have time for extra things? Feats like TWF and Cleave specifically add attacks, but one cannot use OTHER feats when using Whirlwind, correct?
One can certainly use other feats when making a WWA - like weapon specialization and weapon focus, for instance - you just can't get any bonus or extra attacks,
but only so long as the restrictions on WWA hold. If the restrictions on WWA run out before my full attack action does (which is what the other side is arguing), then there is no longer anything preventing me from using them.