Windows 7 - nvidia gt 430 question

core clock. shader clock and memory clock in msi afterburner does any of those option improve video quality if incrase and which one

also how come when i am on the destop my core clock and memory clock go down to 50 mhz very low but if i play a video it goes back to normal is this normal

Either MSI Afterburner, EVGA Precision or RivaTuner are fine for OC, just use the settings to overclock.
OC a little at a time & each time do a test with Furmark or EVGA OC Scanner to check for high temps & artifacts.
Don't overclock too high at once, you'll instantly burn your GPU.
Here's a good place to start: A guide for overclocking your gpu

It's perfectly normal, when on desktop the card doesn't need to run at full speed, but speeds up when playing games or video. So don't worry.

i overclocked it bit by bit to 870 mhz for the core and 1700 for thr memory core it when fine in the furmark but when i played a hd 1980 / 1080 on powerdvd the kernel message came up in the tray icon says driver and stopped and recovered successfull so i clocked it to 800 mhz and 1000mhz do you think then 800 mhz and 1000mhz is good keep in mind at 870mhz and 1700mhz there was no artifacts and no high exessive temp

What's the graphics card brand & stock speed? Driver version?

stock speed core clock 700 mhz memory clock 900mhz so i overclocked it to 800 mhz memory clock 1000mhz memory clock it is working fine coz i cannot but it up to 870mhzcore clock 1700mhz memory clock ps brand zotac
nvidia gt 430 and driver 8.17.12.7533
also ran two test with furmark ran two test with this one 5 mins and another 11 mins and no artifacts at all and max temp was 69 c at this overclock=800 mhz memory clock 1000mhz memory cloc

And the shader clock?

yes

would overclocking improve video quality