RAM from Crucial is actually made by Micron Technologies and is very hard to find. The best place is direct from "Crucial":http://crucial.com.
BTW, it looks like the PC4000 is the better by according to "Club Overclocker":http://www.cluboverclocker.com/reviews/memory/crucial/ballistix_PC4000/p2.htm.
It is about the same price as the PC3200 ($130 vs. $128), but is rated to run at DDR500 at CL2.5 (so it will run fine at 250MHz FSB). A nice buy particularly if you live outside of Washington and don't have to pay the sales tax.
The Micron Ram also performs really well on Athlon 64s.