Thanks to a helpful Half-Life 2.net forumite I was pointed in the direction of this webpage which allows you to apply to become a Battlefield Heroes Beta Tester.

After agreeing to a Non Disclosure Agreement you then must go forth and provide some information about yourself including any previous Beta testing experience and a reason for why you should be in the Battlefield Heroes Beta.

I now find myself waiting eagerly for an e-mail which I hope will provide me with further Beta information…why don’t you try?