I work in a K-12 school district and I can attest to the pain of a duel OS enviroment. AD intergration, when it works, is thin at best, they will not apply GPO's or map the home folder. Altiris works as well as any I have seen (LANDesk, Mangesoft, CA all evaluated withing the last 2 years) which is to say there is a gulf between what the sales people say it will do (and how easy) and the reality. We had a consultant in here for 6 months setting up software delivery, updates and AD intergration, when Apple released a new version and AD intergration broke. He left to take a job with Apple and we are back to doing things the old way, one at a time, hand loading software. Deja Vue 1990's.
My advice would be to keep the MACS off your network. If that is not possible, setup a seperate network segment for them, with their own X-server and hire a dedicated tech to administrator it. In our enviroment we have 20-25% MACS and two techs to support them, while 3 of us handle the 75-80% windows side. Unless there is an overwhealmingly compelling reason that you have to have them, avoid them. If you can't, be sure the "suits and ties" understand that they will increase your support costs disproportionetly to the number of computers. Plus the fact they are costing 30% more than a comparable Dell workstation. Plus the difficulty find an experienced Apple trained tech. Plus working with the company. It all delightfull.
Don't misunderstand me, I am not against Apples. If we had an entirely Apple network, I would not want windows machines on there.