Overclocking My Pentium 4. My CPU runs around 48-55C

Thanks in advance for anyone answering.
Well I was hoping someone can tell me what is the safe temperature for over clocking a Pentium 4 1.8GHZ since I have an Old one at home which I want to over clock.
Also I have read posts which say that to over clock it you just need to mess with the FSB, so is this true or should I change something else as well.
My CPU runs around 48-55C these days, and I have to tell you I do have the option to lock agp and pci speed if that is of any help.
