Q: how to install win7 with boot camp beta

What Mac model/year and OSX version do you have? Boot Camp Beta is very old.

Please see System requirements to install Windows on your Mac via Boot Camp - Apple Support.

Bootcamp is bundled with OSX Versions. You will need to upgrade OSX to get a new version of Bootcamp.

Do you want to consider getting a retail CD of OS X version that you need...

1. http://store.apple.com/us/product/MC573Z/A/mac-os-x-106-snow-leopard

2. http://store.apple.com/us/product/D6106Z/A/os-x-lion

3. http://store.apple.com/us/product/D6377Z/A/os-x-mountain-lion

Can you post the Mac Model Identifier? You may be able to use Snow Leopard, but it supports BC v3.0. Check if you machine can go to Lion.

Your Mac also needs to be an Intel Mac, not a PowerPC Mac.