You would need to use augmented records to do this. You place the user home dir path in the augmented record and then on login it will overwrite what is found in the AD with this new home path.

However, remember that the 2 home dirs will be separated and so a link to the Home dir on the Windows partition will be needed either on the dock or on the desktop, unless you want to keep them separate.

Also bear in mind the potential for confusion.

How you go about Augmented records though is a different matter. I only looked into it briefly when 10.6.3 came out and supported it. Never got mine to work (Apple-IM Handle attribute) but that doesn't meant o say you won't have better luck. TAke a look at the Apple education/Enterprise how-to videos on their site. I'm sure I saw an augmented records video on there.