Intel pentium d overclocking utility

hi ,
i am having old pc with intel Pentium 4-2.26GHz Processors.I wanted to overclock it can some tell me how safely i can do that and what is end limit for it.suggest me good utility to do that.
thank you.

i am using safe and most trustful tool to overclock which is cup-z and gpu-z most time onother toll i prefer to overclock gpu is rivatuner .
CPU-Z is a freeware utility that gathers information on some of the main devices of your system. CPU-Z does not need to be installed, just unzip the files in a directory and run the .exe. In order to remove the program, just delete the files. The program does not copy any file in any Windows directory, nor write to the registry.
cpu
* Name and number.
* Core stepping and process.
* Package.
* Core voltage.
* Internal and external clocks, clock multiplier.
* Supported instructions sets.
* All cache levels (location, size, speed, technology).

you can use all this tools as Intel pentium d overclocking utility for overclocking Sysmark, SiSoft Sandra CPU & MultiMedia, PCMark 2002, 3dsmax-01, EVEREST Ultimate Edition, Prime95 V25.4, ATI tool, rivatuner , gpuz, cpuz, 3DMarks 2001 SE,

Overclocking/Tweaking Utilities

• ClockGen
• RivaTuner 2.0 RC 15.8
• Coolbits 2.0
• nVHardPage SE
• ATI Tool 0.24
• PowerStrip 3.60
• NVTweak
• RadLinker

PC Overall Performance

• PCMark05
• PCMark04
• SiSoft Sandra 2005