I get 140 Mhash\s is there a way to get more?
Maybe. Figure out exactly which card you have so we can compare more easily. Also the wiki-page probably lists the "Golden" examples of each GFX (someone with a low score is less likely to post the score)
Which program do you use to mine?
On the wikipage search for 6850 (
https://en.bitcoin.it/wiki/Mining_hardware_comparison#Popular_Mining_Cards) and you'll see some suggested settings. Also search on the forum
(ok I must admit I can only give advice on cgminer and not very deep either sorry.)