Which Adobe product exactly?
You cannot take a CS5 Windows serial number and use it on a Mac without transferring the license
http://helpx.adobe.com/x-productkb/policy-pricing/order-product-platfo rm-language-swap.html
However that procedure only applies to current versions of the software. So, in short, you cannot put your CS5 Windows onto a Mac with your Windows serial number.
So your options are to upgrade to CS6 for Mac or join the Creative Cloud.