Open IE7 and click on Tools in the top left. Drop down to Internet options and then click on the Programs tab. Set the E-mail to what eva .... then Apply.
Hope thats right
Obviously you don't use a email client like Thunderbird, Outlook or Outlook express.
When you click an email shortcut in IE it's going to try and open up your default email client to send the email.
YOu can setup outlook express with Gmail. If you don't want to use an email client just copy the email.