There is nothing wrong with overclocking your cpu, gpu and ram. Use rivatuner to overclock your gpu because it also has a fan control the catalyst does not. But catalyst has temp monitor and artifact testing which is good. Memtest is something you should use as well to stress your memory and find out if you have any errors. Everest is a great tool for stressing your cpu among other things. pcwizard08, 3dmark 05, 06, and (if you have vista) Vantage are great benchmarking tools. PCmark 06 is also good to have. If anything begins to over heat, your first solution is to get better cooling heatsink/fans, and a good thermal compound the arctic silver.
If you have any errors during memtest (you should use memtest overnight to get a good idea how well your ram is doing. One error is too many) that means your fsb is too high and should be lowered.
Also keep in mind when you overclock your gpu to over clock one thing at a time and test. Core clock first, Shader second, memory third. Also, when changing fan control I would start it at 100% and move it down until the noise lessens but it keeps the gpu cool. Mine is at 75%