I had absolutely no experience w/ domains, forwarding, redirecting and CNAME stuff. Within 5 minutes of reading your .pdfs, I have 2 domains, forwarded, masked and looking good. Big thank you to Mister Ed.
For your information you don't have to forward your domain name in order to host on your mobile me account. You can just change your CNAME to be web.me.com. It would be Alias = www points to = web.me.com. Anybody who clicks on your domain name would go right to there. Mobile me would be automatically masked.