Hi stash152,
You cannot use a Windows version of Master Collection CS3 on a Mac.
The platform swap policy is applicable for the latest version of the softwares and inapplicable for the older version.
Please refer the KB : http://helpx.adobe.com/x-productkb/policy-pricing/order-product-platform-language-swap.htm l
I would suggest purchasing a subscription to the Creative Cloud as the new Mac you bought has Mavericks OS which has not been tested with CS3 and you might face compatibility issues.
The latest Creative Cloud version of the softwares are perfectly compatible with the latest Mac OS (Mavericks).
Regards,
Rave