For anyone else who may be reading this thread, I'll lay out the necessary basics in the simplest terms I can so you can get started. Overclocking can be very simple and safe. Or it can get pretty complicated and even risky. For more detailed info check out the link at the end.

Just follow these steps:

1. Using the App Manager, install these 3 packages:

rootsh
Enhanced Linux kernel for power users
Enhanced Linux kernel for power users (settings)

The Enhanced kernel (thanks to Titan) will allow you to set various clock speeds, custom voltage profiles (like 'ideal' 'ulv' 'lv' and more) to try and save power and many other parameters.

2. The phone will need to reboot to install the new kernel. It should restart perfectly normally.

3. Open the terminal app and type:

sudo gainroot

Hit enter. The prompt will change from '$' to '#' meaning you now have root (administrator) privileges, so be careful!

4. To set clock speed lower and upper limits, start with a conservative setting. Type this command:

kernel-config limits 250 750

You should get a confirmation that the specified setup has been loaded.

5. Congratulations! You have just overclocked from 600Mhz to 750Mhz!

If you have no problems running at 750Mhz, you can re-run the kernel-config command and increase speed as to much as 1.15Ghz, but some units will not tolerate the higher speeds. The phone may become unstable and there is a slight possibility of damage. To stay on the safe side, I'd recommend a max of around 850Mhz.

6. To set one of the lower voltage profiles (for example, 'ideal') type:

kernel-config load ideal

The 'ideal' profile is fairly severe. Again, stability may be an issue with the more radical low voltage profiles. If you have problems with playing or recording videos or anything else, try loading a more conservative profile like 'ulv' (more conservative than 'ideal') or 'lv' (even more conservative).
Note: the 'ideal' profile has a lower speed limitation of 500Mhz, it will not run below that speed regardless of limits you may input.

7. To save your entire configuration so it can be reloaded with a single command, type:

kernel-config save <name>

You can then reload your saved configuration with:

kernel-config load <name>

8. If you reboot the phone, as a safety feature it will by default return to the standard 250-600Mhz limits and standard voltages, etc. You need to re-run the kernel-config commands to overclock again.

9. To make your custom configuration the default settings, even after a reboot instead of loading standard settings:

kernel-config default <name>

10. Many other options besides clock speeds and voltages can be specified using Titan's enhanced kernel. For more details check this out:

http://wiki.maemo.org/Overclocking