Using iCloud Mail account from Computers without Lion?
The short answer is you get to keep MobileMe as it is until June 30, 2012. 

Sometime between when iCloud launches (tomorrow?) and next June, you can choose to learn about and use iCloud (assuming it meets all your current and future needs) or find another email provider. 

It is clear that Apple has said you will lose access to you me.com account if you don't move to iCloud by then so unless that changes, you should plan some action. 

If things go as planned, we will all get a public look at things this week. Perhaps read some official documentation in the next month you. The future is unclear today before iCloud has launched, but you have 9+ months to worry about this...