The sticky to the link to Eva2000's post is complicated as hell. I'm pretty good at overclocking and even I don't fully understand it. There are a lot of better guides out there for beginners.
As for the memory thing, what kind of memory do you have? We might be able to determine how high it can be overclocked.
If the memory sucks for overclocking, then you would have to set a memory divider through either your BIOS or, I think A64 Tweaker also has an option for memory divider speed. It will set your memory speed at a ratio to your HTT/FSB. So, if you have a 6:5 divider; For every 6MHz of your HTT/FSB, your memory will run at 5 MHz. So if you HTT/FSB is at 250, the memory will be at 208...stuff like that.