You've not said which e-mail client (Outlook? Outlook Express? Thunderbird) you're using, or whether your e-mail contacts are stored with a web-based mail service.
This will work for Outlook Express (and probably for other mail clients as well):
Click on 'Addresses'
If necessary, click on a relevant folder, in the left pane. (You'll probably find that 'Main Identity's Contacts' is already selected anyway).
In the right hand panel, click on one of the contacts you want to forward. Then, while holding the Ctrl key down, click on each of the others in turn.
Right-click on any of the highlighted contacts and select 'Copy'.
Click on 'New Mail' (or otherwise start a new message to your friend). Click to place the cursor in the message area, then right-click and select 'Paste'.
Chris