Thanks to mOmA for this tip!

For everybody who wants to know the basics of fonts:

There are three formats, Postscript, TrueType and OpenType. First there was Bitmap only, but these are gone by now. PS is the original one, invented by Adobe. TrueType was invented by Apple, but ironically, these fonts are now the major font format used under Windows. PC-Truetype fonts differ from the original TrueType format Apple used, therefore TT-fonts can't be swapped between the two operating systems. That's where OpenType comes in, a new format developed by Adobe and Microsoft in cooperation. This one won't be much different to PS, but it will bring together both, Postscript and TrueType into one single font-item. No extra suitcases. Just the font. The second big difference is these fonts can be used on both PC's and Mac OS.

Postscript fonts:
Using PS fonts, you always need two items, a Postscript font with an icon similar like a laserprinter (Adobe has a big A-icon instead) and a suitcase with the letter A on it. Both of these go to the system folder into "fonts".

TrueType fonts:
TrueType is being used on Windows- and Mac OS-systems alike, but even if it's the same format, it's not the same thing. Unlike Postscript fonts, TrueType fonts can't be swapped. That's why they came up with OpenType after about ten years of thinking... ;)

OpenType fonts:
Considering what Adobe claims and being aware of the power of MS on the market, OpenType could become indeed the best solution for us all. There are only two drawbacks: Adobe is slow in releasing OpenType fonts and untill Adobe Typemanager Deluxe 6.0 comes out, there won't be a way to convert existing fonts (TT and PS) into the new OpenType format. Microsoft at the other side has announced to use OT on their systems instead of TT, but so far Windows 2000 is still being sold with TT fonts.