Actually, if I didn't war game I'd probably use macs myself for home computing.
I don't think any of the JTS/HPS games will run natively on a Mac (the game executable file is a windows .exe type and the graphics are windows bitmaps) but there are 2-3 possible workarounds to running it on a mac:
1. Dual boot the mac - the new ones have intel chips and so can run windows. I believe the Windows installer will detect the existing operating system and offer options to install it onto another drive. When you boot up you should have an option to select OSX or Windows. I used to dual boot Linux and windows years ago.
2. Run a Windows Virtual Machine on the Mac. This requires the VMware (which your son may already have) and probably a licensed copy of windows. With this method they can stay within OS X and just run windows in a window when they want to play the game. (If they have a spare unused PC with windows on it, then the SN for their copy of it can often be found on the case and is valid for reinstall.)
3. I've never tried this one but found the solution online. It looks promising:
"Running Windows apps directly in Mac OS X -- without Windows. CrossOver from CodeWeavers runs Windows applications directly in Mac OS X, without using Windows. Because you don't need to own a copy of Windows, CrossOver is the least expensive way to run Windows programs on a Mac. The trade off is that it doesn't run every Windows application."
Here's an informative link on all three methods:
http://www.macwindows.com/winintelmac.html
Hope that helps!