You could underclock your PC. I know that some games, specifically older ones, run faster or slower depending on your processor (the game speed is directly proportional to your processor's speed). P2 was out when there were 486's (i think), so running it on a 1Ghz machine is like putting a ferrari's engine into an old VW beetle and then flooring it.
other than that.. uhhh.. I really don't know. I could always be way off on this one.
There are some programs you may use.
Primarily intended for emulation purposes I belive.
Mo'Slo; there is an older Version that's trialware, can be found here:
Other games just run as fast as they possibly can. One solution there is to run a program that wastes your computer's processing at a steady rate, or other tricks and there are PD programs specifically for this task. For example, one program for this is called MOSLO, but there are others.