One easy way is to right-click on the NEF image, select "send to", "email recipient", then a box will pop up asking you what resolution you want to send, and guesstimate the size of the file(s) you have selected. After that, your default email application opens with the jpeg files already attached to a blank email. The NEFs are unchanged.
In XP, I had to add the NEF thumbnail update, but it seems Windows 7 knows all about NEF.