i use Afterburner. it seems a bit less complicated then Rivatuner. but both are fairly good programs.
do you overclock a CPU? im a bit confused what your asking. but if your question is DO you need to overclock the CPU to overclock the GPU then no.
GPU overclocking is pretty easy compared to CPU overclocking, also download Furmarkhttp://www.ozone3d.net/benchmarks/fur/
this will help you make sure your GPU temperature is stable by running a stress test to see how hot it gets. i would also get HWmonitorhttp://www.cpuid.com/softwares/hwmonitor.html
which is another temp monitor that i usually leave on most of the time just so i can see my highest GPU temps after i finish gaming.