1gig vs 2gig ram

i am building new computer and wondering if i should get 2 gig ram? i will get very good memory...i was looking at this one. http://www.newegg.com/app/viewProductDesc.asp?description=20-144-161&depa=0
will my computer ever use more than 1 gig? i just do normal stuff and play games. is there better memory i can get? i do not want to overclock.

Well. what are you building? that is very good ram if you dont want to overclock, but you can certainly get cheaper. PQI, GSKILL or Kingston value ram would probably work for stock too and cost less.
I saw some KVR down at my local shop that has -5b G chips.. if i had the money.. omg. that stuff seems to be able to reach 2.5-2-2 at ddr 500. overkill for you not wanting to oc, but you can run the timings down on that at ddr 400 and get kickass ram for not much money.
athlon 64 or p4?

but as for 1gb vs 2gb.. i just went from 512 mb to 1gb and that difference isnt so pronounced.. it allowed me to tweak a few more windows settings and get a more studderfree gameplay experience, but anything over 1 gb is not required unless you run a 24/7 server that is memory intensive. 3d rendering apps and databasing needs memory mad, but still not enough to really see a big difference between 1-2 gb.

athlon 64. this cpu needs 400 mhz ram right? but what if i bought 500 mhz ram...would i notice any increase in performance? or will it just hit a bottleneck and be wasted. is it possible to get memory better than 2-2-2-5?

Apparently athlon 64's have a pretty good spectrum of dividers, but i think as with any platform, you want to try and run your ddr and system at 1-1. athlon 64 is 400 mhz fsb dual channel if you get a new one so ddr 400 2-2-2-10 *tras 10 is the best for nforce 3 and athlon 64* would be your best bet. that ram you linked to would do that. all you have to do is change the tras setting to 10 int he motherboard bios.
ddr 500 wouldnt be of much use since you arent trying to overclock your athlon system to ddr 500. you can of course run the multiplier DOWN on athlon 64's to attain a fsb of 500 mhz.

If you do not plan to overclock, you definatly want the tighest ddr 400 possible to run with that athlon 64. that memory you linked to uses the latest samsung tccd chips which are rated to ddr 500, so you can overclock if you so choose later on. I suggest the pqi if you can get it. the egg has that stuff. its cheaper and gives you the same thing.