You never have to "install" an e-mail program first off Windows comes with a basic one built in. The best way though is just log into what ever e-mail you have yahoo or gmail or whatever through the internet. for example gmail would be mail.google.com login hit compose then look for the paperclip that says attach file next to it. Click that pick files you want to send and off they go.
Actually, Windows 7 doesn't come with an e-mail client straight out of the box. If you want an e-mail client you have to download one. I think it has something to do with legal actions taken against Microsoft that prevents them from bundling some software with Windows in certain countries. The Microsoft e-mail client is Windows Live Mail 2011. A couple of other ones are Thunderbird and Eudora. Alternatively, as stated above, use a webmail service like hotmail or gmail, those don't require an e-mail client.