Your links don't work. If you want the best you can get the 2gb OCZ PC4000EB or 2gb Mushkin Redline PC4000. The 2gb Crucial Ballistix have been problematic check out James's link and there are several reports on various forums about dead sticks.
The Opterons do work in DFI boards they're just not "officially" supported. I woulden't get any kind of Crucial memory for a DFI board. DFI-STREET has a recommended ram list for the DFI boards. Mushkin, G.Skill and OCZ all do fine on them. I personally use the G.SKill 2GB PC4000 on my DFI Lanparty UT. However I have heard of some people getting bad G.Skill 2GB kits I don't know though it always seems to be the "I had a friend, who knew a guy that also knew some people that had trouble with it" I haven't had any problems and neither has the guy on here with the same kit. And Newegg and G.SKill have excellent RMA process anyway.
Memory speed on A64's isn't too important though and you have a 146 and a CABNE so you'll need a divider even with 250mhz memory (if you're overclocking and you damn well better with a CABNE). I'd probably just go with a solid PC3200 set.
Gaming/Work Computer: << AMD 3700+ :: DFI NF4 Ultra-D :: 2GB (2x1GB) G. Skill :: Evga 7800GT :: 36GB Raptor :: 485w Enermax >> File/Print Server: << AMD 1600+ :: ABit Mobo :: 1GB (2x512MB) :: 1 x 60GB IBM : 4 x 120GB Maxtor :: 3 x 250GB Maxtor :: 2 x 300GB Maxtor :: 400w Antec :: Total Storage: 1.89 TB >>
You're going to have to tweak the DFI to get to DDR500 at 1:1 or more but you also get tight timings if you have good memory (Be prepared to spend some time on it). On the other hand no tweaking and I got to DDR500 everything auto and then to DDR520 and beyond with some minor tweaking but you have loose timings. My cpu topped out at 2.6ghz but I could definitely get more from the ram.