I am buying a 32 version of the DT770. Is this better or worse than a 80 or even 250 version? I also only have a motherboard soundcard, but you suggest I get a Soundcard or AMP? In that case, wich one? I have also concidered other headsets but I hear this one is best for PC useage in this priority Music;TV/Movies;Strategy Games;FPS games?
The matter of sound quality between the various 32/80/260/600 versions is debated on these forums an honestly not something to worry about. For your purposes, since you're using an onboard soundcard the 32 ohm is the best bet as it will be the easiest to drive and bring to reasonably loud levels.
If you have an extra $100, a combo dac/amp like the Nuforce uDac2 or HotAudio DacDestroyer are excellent little units. But if you don't have the budget for it, don't worry about it. It'll sound just fine coming our of your computer.
Its hard to say which version to get since Beyer makes slight revisions to their models all the time and doesn't tell anybody. The most consistent differences seem to be between the Premium and Pro versions and among the ones I've heard I like the premium versions better and even the 250 is likely to be fine from an onboard.sound card.
If your current sound card doesn't have some some sort of headphone virtualizer or just has a crappy one I'd recommend a sound card with that feature over an external DAC/amp. The gain you'll get when when listening to 5.1/7.1 sources will outweigh the small advantage you'll get from even top quality DAC when listening to plain stereo music.