i guess there's nothing wrong with bsplayer itself :)
bsplayer can change the resolution of your screen ... but not the resolution of your movies ;)
what's the resolution of the so called "very bad quality movies"?
if u try to display a low resolition movie - e.g. DVD-like (720×480 NTSC or 720×576 PAL) - on your 1680x1050 tft ... it's obvious, that it's unsharpen or/and smooth in fullscreen or maximized window mode ... ^^
maybe the Haali Renderer can help to solve you problems with low resolution movies ( part of Haali Media Splitter:
http://haali.cs.msu.ru/mkv )