Ok, here is a very basic rundown.
There are a few components to worry about. Core Multiplier, FSB frequency, and memory dividers.
FSB relates to the 2.6ghz because you most likely are running with 200mhz FSB, which would mean the core is then multiplied by 13. By increasing the FSB to 205mhz, your processor would be running at 2.665GHZ instead of the 2.6 it's running at now.
Take these steps to insure safety!
1. get a good temperature sensing program, such as HWmonitor
2. Make sure your core temperature does NOT exceed 65c (I keep mine under 50c load)
3. Download and run Prime95 for an hour or two after each step to ensure that everything is stable.
4. DO NOT jump the gun, overclock the FSB very slowly, 5mhz at a time should be fine. If you get ahead of yourself you could end up damaging something.
I haven't a clue about the memory dividers in a Pentium 4 system, and it may very well be memory multipliers in your case. If your system ends up unstable after an overclock, you may want to reduce the ram multi, or increase the divider accordingly. This way you prevent the memory from becoming any sort of bottleneck.
Also, HyperTransport plays a part, but I am more familiar with AMD overclocking. Treat the HyperTransport just like the ram. If your system is unstable try reducing the HT speed slightly, and try again.
Also, I appologise for not reading the abit motherboard part of your first post, I'm not sure how I missed it but hopefully this reply will help.