The heatsink and fan you have, did it come with the CPU? If it did, it's more than likely stock. It's usually aluminum with a green fan, but these days that might have changed. When you overclock, things heat up...and you'll need a better heatsink and fan if you want to overclock ALOT, or if your ambient temperature is just abnormally high.
Your motherboard is thankfully an ASUS, you shouldn't have any problems with locked BIOS or low overclocking limitations. Overclocking is all done in the BIOS, you access this when you boot the computer.
Your RAM is PC3200 which is great, but there is a little bit more you need to know before you start overclocking.
I suggest you read the guide I posted up in my first response to get a good idea of what all is involved and the basics of getting into the BIOS and making yourself familiar with all the different menus.