Hi,
iTunes automatically uses the first account set up in Mail Accounts so delete the Mobile Me account.
Or:
To set up a Photo Mail account:
Choose iPhoto > Preferences, and then click Accounts.
If you’re in full-screen view, move your pointer to the top of the screen to make the menu bar appear.
Click the Add (+) button in the lower-left corner.
Click Email, and then click Add.
Choose your email service provider.
If your service provider isn’t listed, choose Other.
Type the requested information.
If you use the Mail application included with Mac OS X, some account information might be filled in already. If you’re not sure what to type, contact your service provider.
You can set up more than one iPhoto Mail account by repeating these steps for each account. When you send an iPhoto email, you can change the outgoing account by clicking the From pop-up menu and choosing an account.