First, if you won't "free" fonts I recommend you
DaFont.
As long as we are talking about installing and bundle with software here you have what you can and can't do (in a simple way) with the fonts...
Public domain: You can truly do whatever you want.
Free: You can do whatever you want with it, donation is not available through the page you are downloading or author doesn't ask for well deserved retribution.
Donationware: You can do whatever you want with it, donation is available through the page you are downloading or author ask for well deserved retribution by other means.
Free for personal use: You can use it, you can't bundle with software, you can always buy a license, the price depends in the use generally, you can even get a "license" free sometimes, others it's as low as a dollar, a symbolic donation.
"Pay or Die": Basic (5 Pcs) / Site License (fixed number of Pcs in given locations) / Corporate License (basically you can bundle with the software, no limit of Pcs or related). This are usually pretty expensive.
Once you have the font installed in your system you can use it in any graphic work you do, commercial or whatever, font still cannot be bundle.
But there are some loopholes as always, for example the best Unicode fonts are expensive as hell if there's even the possibility of buying a license, the best in my opinion are from
Adobe, and they don't have corporate license.
But many of them are bundle with basic software from adobe, like adobe reader. So all you have to do is point to the path were the fonts are installed and you are clear, you didn't bundle and you are not violating any license, you can do the same with any font bundle with Windows or whatever. The only problem could be when user doesn't install in the default path, for what you could use a fallback anyway. Pity XBMC doesn't allow this or I didn't find a way of making it happen.
