In order to know how many pipes the GPU has running requires more than just a number. We need to know the manufacture of the card and its model number. Typically the x1900 has between 12/36 and 16/48 - PPL/PSP depending on the core and manufacture.

Unlocking pipes depends on the same. Some cards can not be modified or hacked at all. Some cards will allow a mod from Windows software such as Rivatuner and others require a BIOS mod and flash + Windows software hacks. If you dont know what you are doing, both can be dangerous although usually making changes through Windows software is reversable. I do not think with ATI cards it is possible to hack pipes in Windows. I know some older Nivida cards can. Usually ATI requires a modified BIOS to unlock pipes if it is even possible.