I have fat fingers, I ALWAYS have problems changing fans around. Some are tougher than others.
However, esp with more recent processors, the heatsink/fan mount is standardized. Find sometehing that specifies for p4, and you're good to go.
Look for reviews, especially places like Tom's Hardware, that talk about quiet PC systems. They often have good nuggets of advice that let you find a fan that isn't so quiet it's expensive, but does what you want at a reasonable price. Usually I look for reviews from 3 sites or more, and average the reviews.
And Raybay, WTH??? The more expensive the more difficult? Where in GOD'S name did that come from? Evidence, links please?
It's late here tonight- if someone hasn't found you good reviews by tomorrow, I'll try to dig some up and link them here.
Late PS- I've never worked with it at all, but I hear for the ultimate in quiet as well as great temperature control, water cooling is worth investigating. The concept of putting water near the electrical makes me nervous, though...