Can't find a GT 335M, but the comparison list at https://en.bitcoin.it/wiki/Mining_hardware_comparison appears to state that a 330M will mine at about 7 MH/s.

You can try overclocking, but something that really helped me is to use the GUIminer and run the CUDA miner. My Nvidia GTX 460 hits 60+ MH/s. It still has absolutely NOTHING on the HDs from ATI, but I didn't have to pay anything extra for it.