Well, Hey there fellow Quebecer.
I can't really help you to choose the best ram, I don't have much A64 knowledge yet, plus I don't know all of Corsair's model terminology. I *guess* PC3200 (400mhz) sticks would be fine enough, if you don't plan some heavy overclocking.
But just wait to get other input from the others, just in case...
I had a quick look on the Corsair website
, they say CMX ram (which MicroBytes sells) IS in fact, XMS. If you are on a budget, and won't be overclocking, I guess "basic" Corsair sticks would do though.
Total amount of RAM is up to you, if you plan running on dual channel (DDR) if your mobo supports it, get some TwinX kit. Whether you choose this setup or not is up to you, I don't know if Dual Channel shows big improvement on A64 systems, just look for some reviews if you want.
Oh, and don't get ECC ram, unless you need it. If you need it, you'll know why.