Now, Apple has published a couple of Knowledge Base articles designed to help you if you get some mail that might not really be from Apple.
The first posting helps you to renew your account, update your credit card information, and to deal with messages MobileMe may send you about your storage limits.
It also has an additional older specific link to help you identify fraudulent emails that look like they are from Apple but aren't. For whatever reason, crooks love to prey on MobileMe users, and there have been issues with fake renewals and credit card phishing schemes for a couple of years now.
If you have any doubts, check the Apple articles, and report any problems to Apple. A credit card is a terrible thing to waste, or lose.