Its really a waste if you ask me.
That zalman would best be used on a system that you OC.
That cheap Aero on my Tbird which runs hotter then my dads XP, is currently folding. It has been running 24/7.
My Room temp is warm, 82F.
And on full load the Tbird is sitting 58C, idle was 53C. (side case on)
If my room temp drop back to 70C, it would be 52-53C full load on folding.
I'm guessing it would be cooler on that P4.
But what evah, go ahead and spend your parents moola. Don't know why you asked for advice.
edit: Also even though you can re-use the Zalman on another system, your just goin to put that other HSF back on? You could use that machine for somthing useful, and have something decent then what it has for HSF.
And depending on what new system you build later on in the future, you might find something better then the 7000.