to 'My Computer' because it isn't a location - it's simply a graphical representation of the hardware locations to which you can save data.
I think that you probably saved the file to a folder in 'My documents', and you can attach it to an email in Windows 7 in just the same way.
Compose your email, and then look for the 'attach' icon in your email software - it usually takes the form of a paper clip. Click the icon, and then use the browsing window that will open to locate the file you want. Click on the file and then click on 'open' at the bottom right of the box - the file will be attached to your email, you'll see an icon for it appear there.