The font we chose is called "Tahoma". It's not the best font by any means, but it has one critical factor that no other cross-platform font has : that it's the same height on both mac and windows. There are some more documents about this on the GoyaBlog, but basically, you've got 11 choices for a default installed font, and none of them are the same on mac and windows.

However, if you assume that the user has some other microsoft software installed on the mac such as office, then you also have the option of using Tahoma. If you don't have office and don't ever plan to install it, do a google search for "download tahoma font mac" and you'll find plenty of places you can get it from.

Also, if you're not worried about the look, it won't affect how well the software works.