Adobe created a document that walks through the process of emailing images from Lightroom:

http://www.adobe.com/cfusion/knowledgebase/index.cfm?id=333743

Some quirks have presented themselves on Windows with certain email
clients. However, another Lightroom user and programmer (Steve Sutherland) created a little application that can make it work. I’ve installed it myself and it works like a charm.

– go to http://lightroom-extra.com/
– click the Download section
– click the bottom link on the Downloads page (“Other Goodies”)
– download the MAPI mailer zip file
– unzip and read the instructions included
– install the application

Give it a test and you should be in business. The application
essentially facilitates the sending of files from Lightroom to your
default email client. I have used it on XP and know of at least one person who used it successfully on Vista.