Switching from Windows to Mac

You can run Windows using emulator software like Parallels or Fusion running Windows XP or perhaps Vista. You may be able to install Vista using Bootcamp. Under Mavericks I am sure XP is no longer supported.

Unfortunately no.

Creative Suite serial numbers are platform specific: Windows only or Mac only. So you cannot merely install CS3 for Mac and enter your Windows serial number. Won't work.

There is a platform swap process to swap from Win to Mac or vice versa but it only applies to the current version (CS6)

http://helpx.adobe.com/x-productkb/policy-pricing/order-product-platform-language-swap.html

Also CS3 is too old to qualify for an upgrade to CS6.

So your choices are:

Buy a new copy of CS6 Mac

Or join the Cloud. As an existing CS3 owner, you qualify for the honeymoon rate of $29.99/month for the first 12 months. Full price thereafter.

http://www.adobe.com/products/creativecloud/buying-guide.html

Or join the Photoshop Photography Program (PS CC + Lightroom 5 + extras) for $9.99/month (subscription only)

https://creative.adobe.com/plans/offer/photoshop+lightroom

Or if your requirements are simple then consider buying Photoshop Elements 12 (Photoshop's little - but powerful - brother). That comes with a serial number which works on Windows and/or Mac.

http://www.adobe.com/products/photoshop-elements.html

Or buy Lightroom 5 for Mac if that does what you want. You don't have to subscribe to Lightroom, you can still buy it outright and, again, the serial number works on Winbdows and/or Mac.

Or run CS3 Windows in Parallels on the iMac.