Save it with the file name:
"viaagp4xon.reg" (without quotes) and run the file to edit your registry.
Be aware though that the P3V4x can be unstable at AGP4x and that is why it`s disabled by default beginning with the 4.16 nVidia drivers. If the drivers detects a VIA (Apollo Pro) chipset, it defaults to 2x.
I have a P3V4x and the difference between 2x and 4x is minimal at best (a couple of FPS on ocasion) and not worth the potential unstability.
On mine, I ran a GeForceDDR at 4x with absolutely no problems. Now, I`m running a GeForce3 and have to run at 2x due to some unstability.
Some games will run fine at 4x and others will simply not run.