AMD overdrive will display the temps of the CPU and GPU. Its voltage monitoring doesn't work for me and I have never used it except as a monitor. By definition I don't trust software overclocks of the CPU as it is meh.
For the GPU the catalyst control panel will handle it for you. For the most part you just let it run, then back off 10-20 mhz from where it OC'd it. It can take a loooong time, and you need to disable your screensaver. Just note this is risky and varies greatly depending on the GPU's cooling. I am running my 4890 at something like 890/1000. The OC tool spit out an unusable 925/1050 that caused glitches and blue screens.
For CPU the best bet is bios. If you have a black edition you can just bump up the multiplyer in increments of 0.5 until you bluescreen; try upping the voltage a tad and repeat. Modern boards will lock in the memory for its respective speed, so it is less annoying and requires less calculator work and fidgeting.
Just double check your junk before applying it, back off a tad after you reach "maximum" and make sure to test the OC thoroughly. Also don't be surprised when your vid card and/or motherboard give up the ghost without warning. Note that if your temps go up your OC can cause stability issues, so if your room is bone cold in the winter and hot during the summer it has the possibility of impacting things. Also make sure to write down the settings once you are done, as the BIOS loves to reset at inopportune times.
