that requires a cross-grade.
but i'm not sure that's available for cs2: http://helpx.adobe.com/x-productkb/policy-pricing/order-product-platfo rm-language-swap.html?PID=2159997
What kglad said.
Although crossgrades (Windows license to Mac license) are available, they're only for the current version (currently CS6).
Since CS2 is not eligible to upgrade to CS6, you'd have to purchase a new full version of CS6.
Your most cost effective option now is to join the Adobe Cloud where the license permits two installations per membership and is multi-platform - Mac and/or Windows, no crossgrade required.