Well getting the most out of your system is what this site is for. My question is what do you want performance for? You are going to be limited in what you can do, especially with pc2700 ram and a radeon 9200se. I know you don't want new hardware so I won't go there. As far as overclocking your processor you will either have to see if you can lower your mem to run at 133mhz (pc2100) or you will have a very limited overclock on the processor, but I wouldn't recomend this because you will most likely lose performance.
Your fsb setting in the bios is what you want to change. The default is 166MHz, I'd say try going up starting at 170, then 175, and so on. Each time let the sytem boot into windows and if you encounter any instability then up the vcore on the processor. Default should be 1.65v and you should be fine running it up to 1.8v with standard air cooling. Go up in the smallest increments you can, 1.675,1.7,1.725,1.75, and so on until it's stable at your speed. If you're up to 1.8 and still having trouble, try relaxing the mem timings on that motherboard (if the option is available). WHen I talk about mem timings I'm talking about things like CAS Latency, RAS to TAS, and all that fun stuff.
If you're looking to overclock the graphics card then download ATi Tool here
http://downloads.guru3d.com/download.php?det=725 and install it. I'd suggest going into the ATi control panel and turning all your graphic quality settings at high and turning AA and AF on. Then run ATi Tool and select find max core...this will help you find your max core overclock. after you figure out where ATi tool says your max core speed is and it runs at that speed for I'd say at least an hour then write it down, remember it. Then return the card to default settings. Then click "Find Max Mem" to find your mem overclock. NOTE:While this test is running it's good to watch yourself for artifacting (corruption in the image). ATi tool is pretty good at catching this but it's not 100%. You know your OC is good when the image doesn't get corruption (artifacting) and the system doesn't freeze up or crash any programs (including windows).
Those are just a few tips on overclocking your new rig. I hope you get some good results but they may not be like some of us get here. If you had pc3200 ram you'd have a much better chance for a cpu overclock, I definately wouldn't want to drop my ram down to pc133 on an athlon xp system just to OC it.