I really, really wouldn't bother. But what 3.40mhz chip are you talking about?
Heres a data sheet with processor upgrade information:http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&docname=c01324212#N92
But like I said, you're basically replacing an old ass CPU with another one. If you're paying retail for this upgrade, don't do it. 20 bucks on ebay, sure what the heck?