Did you get Directory Access to bind with Active Directory? If you're connecting to the primary domain (ex. apple.com), then in the AD Forest you put in apple.com and in the AD Domain you also put in apple.com. Then in the Computer ID you put the name of the MAC!!! NOT THE PC YOU'RE CONNECTING TO!!!! That will create a ******** of problems for you. Been there done that! Then click bind. It should ask for a username and password. Put the username and password for the administrator account in Active Directory and it should bind through all 5 or 6 steps.
Let me know if that doesn't work.
If it does work, then click ok and that should take you back to Services tab. Next to it you should see 2 more tabs, Authentication and Contacts. Click on the Authentication tab and then by Search, click on Custom Path, then click on Add. A sheet should pop down and the newly added Active Directory path should appear. Select that and then click on add.
Then click on the Contacts Tab. Under search, click on Custom Path. Then click on Add. Again, a sheet should pop down and the Active Directory path should appear there too. Select that path and then click on add. Then log out and if your have Fast User Switching on then "Other User" should appear in the list. If not then just put in the Username and Password for the user you want to log in as on the AD Server. If you have your login script working correctly on the PC side then your drive should map when it logs in.
This is how I got it working both at home and at the school I used to work at where they had mostly PC's and about 3 iBooks. I got them working with Active Directory where their shared drives mapped upon login. I even had it setup so that everyone got the same Dock Settings with only specific apps when they logged in. If you get everything else working and want to know how I did that, please let me know with a Private Message and I'll get right back to you on how to do it.