but if i have the pc attached to the broadband can i just steam the internet to my my computer which is the mac.

You can, but I recommend very much doing something else instead.

In between your DSL modem and your home LAN, insert a broadband NAT/Firewall/Router box. This will allow the Macs and PCs to all share the one IP address and will also protect you from hackers and such.

They are inexpensive (under $50.00 these days) and are very much worth it because they make everything much easier and less likely to be hacked or to get worms (viruses).