K750 is for imaging nd not so gr8 for music, but has gr8 value for money....around 11k.
W810 i is good for omaging as well as music(walkman series) nd also got EDGE. The speaker is also much louder.But i think it doesn't justice for that price(17k with bill). Around 15 is ok.
Also k750 comes with only a 64MB card whereas w810i comes with 512 MB card. Also 512MB is not so gr8 as u can get 1GB sony pro duo for as low as 1.6k. But u get a high quality earphones with walkmans...which has got very good bass response which is unmatched by any other headphones in the market(in same price range).