The only way I can think of is to swap the clip with a 3 hole clip on either end.
Of course, you might wanna make sure that CPU is still alive before hand.
Off the top of my head, CoolerMaster comes to mind as a company with fairly inexpensive coolers with the 3 hole clips on some of their heatsinks. ThermalTake is another with some of their Dragon and other 'Orb' style coolers. Thermalright also does--but their coolers may be a bit of overkill for a P3.
The other thing to watch out for in the P3's above 1GHz that are Tualtin cored, is that the ones with 512k L2 cache are the only ones with SMP enabled. The 256k L2 cache'd variants will not work in SMP at all---and may be the reason you're not seeing it.
Windows XP Pro (if you have home---that's a big problem right their) Should detect it right away.
Windows NT and 2k will need to be reinstalled before the extra CPU will be seen.
Didn't see this earlier, but welcome aboard!:)