if that gtx 260 has a gig of ram you should be able to crank texture detail to full with the draw distance at a bit above half.
if it only has 512 then your looking at medium texture quality at best.
edit: hm its got the 896 or whatever megs of ram on it. you should be able to jack it up to full quality but view distance may or may not be to your liking.. just depends how you setup the other sliders.