Arial (PC) and Helvetica (Mac) should be avoided for cross platform compatibility due to the same reasons they shouldn't be used on a web page - one looks good and the other looks crap depending on whether you're using a PC or a Mac. As such, it is often recommended that Verdana be the font of choice for website design. I assume this would also be a good course of action in terms of cross platform games/applications.
An alternative action is to take a look at one of the many free font websites, as these tend to offer the same font in both PC and Mac form, so it would simply be a case of making sure you have the right file for the right version of your game.
An alternative action is to take a look at one of the many free font websites, as these tend to offer the same font in both PC and Mac form, so it would simply be a case of making sure you have the right file for the right version of your game.