I am sorry to say this but...
You probly can not oveclock that CPU.
The motherboard is the most important part in overclocking, and Gateway's (all OEM for that matter) Ship motherboards 99% of the time without overclocking options...
The P4 is multiplier locked, so you have to way to change that.
The only otehr way is by increasing the FSB(front side bus). That is done in the BIOS or by jumpers on the motherboard itself. If you board doesnt have any jumpers to change the FSB, you still may be able to overclock the board with software programs in windows.
To do this, you need to find out what clockgenerator your Motherboard is using. The best way to do this is with a program called sisoft sandra
http://www.sisoftware.demon.co.uk/
The other way to do it (i like better) is look on the motherboard itself. The clock generator is a small black chip. It is about 1c wide x 2.5cm long. Very close to it is a silver cap(smaller than the clockgenerator) and shuold have 14.xxx printed on it. the clock generator is located in the top right portion of the motherboard most of the time. When you find out were it is, right down the name and model of it. (ICS, IC-WORKS, WINBOND, REALTEK, are command names followed by the model number) and then post the name back here. Then we should be able to help you out with software overclocking if it is at all posible