I have an XP 2000+ CPU here clocked at a sippin 1.675 MHz and averaging only about 48 to 52 degrees celsius thanks to my beautiful ThermalTake Volcano 9 Coolmod heatsink/fan. I do have 3 other blue LED fans by ANtec that keeps my system cool in an aspire turboserver case with side windows.
Sure, it may be loud enough to drown the modem noise, but then again, I'm deaf.

Although, to tell you the truth I wouldn't mind having a passive watercooling for my system, but if I weren't that scared to put water near my mobo, I would do it in an instant.
Just an recommendation: go for thermaltake - try HC0001 - with the heat pipes on the side of the heatsink - be forewarned, I've heard reports that it barely fits almost all motherboards for it because of the large spherical thing (transistors, I think).
TIGS