What version are you talking about and have you got the serial number?
If you want to install version 11 then you can download from Adobe website and use your serial number to activate it. The only problem I can see is that your serial number might be for a windows system and I don't know if it would work on a Mac. However, it is worth a try.
You are allowed 2 installations simultaneously so you should be OK in this respect.
The download link is here:
Make sure you use the MAC to download it so that you get the correct version for it.
If you mean you have the disc version, you can copy the mac installer disc to the pc, network the two of them and copy the files over to the mac. Or if it's PSE 11, just download the trial and enter your serial number. If you have a boxed version the serial number is good for two installs on either platform or one of each. For downloads, the previous post is correct that a download serial number is for two installations, but both must be on the same platform, so you would need to buy PSE again.