Can the two be combined? I'm not seeing why they couldn't be, but if they can, I'm not 100% sure how it's supposed to work.
Here's the relevant text:
Rapid Attack (Ex): At 11th level, a mobile fighter can combine a full-attack action with a single move. He must forgo the attack at his highest bonus but may take the remaining attacks at any point during his movement. This movement provokes attacks of opportunity as normal.
This ability replaces armor training 3.
Whirlwind Attack
When you use the full-attack action, you can give up your regular attacks and instead make one melee attack at your highest base attack bonus against each opponent within reach. You must make a separate attack roll against each opponent.
When you use the Whirlwind Attack feat, you also forfeit any bonus or extra attacks granted by other feats, spells, or abilities.
So, by my reading, I can use the Whirlwind Attack feat, which is a full-attack action, as written, and combine that with a single move taking my remaining attacks at any point during my movement (!). The only issue with this is Rapid Attack normally must forgo the attack at my highest bonus, but with Whirlwind Attack all of the attacks are at my highest bonus.
I suppose with a very strict ruling you could say that since all of them are at my highest attack bonus, that I must forgo all of the attacks granted by Whirlwind Attack, thus the two abilities do not mix at all. On the other hand, being wildly liberal, one might rule that I merely give up one potential attack against an adjacent enemy and I then can attack all other opponents adjacent to me at every point of my move (since I can take my remaining attacks at any point during my movement).
How would you rule this to work, if at all?