That's not a problem, an HD 6450 only has 160 stream processors. It's not the godzilla of the graphics world. My 3870K APU has 400 stream processors and OC'd to 900Mhz I get 98MH/s. pretty much inline with half a 6770 with 800 stream processors.
That chip with the HD 4000 is performing pretty much where it should.
100mh/s... not bad for a $100 CPU.
Granted it's only ~1.5BTC a month, but it's better than a single core Sempron 140 that you can barely sell for $10 used.