I receive e-mail attachments from a mac and I am unable to open them. There's no 'magic bullet' used to open ANY file. You should know what you are trying to open, and choose an appropriate app to do the job.
Hunters know what they are looking to shoot and use the appropriate gun.
Same goes for you. If you expect a lot of mac files it may be worth investing in this, otherwise just email your friend and ask for simple text or pict or gif or jpeg attachments etc. It is probably easier for the mac sender to make the attachment more PC friendly. To ad them yourself might work. This often solves the problem.