1:AMD 64BIT is good choice.
2: dual channel wont bring significant performance as what u get out of AMD 64Bit
3: dont buy 9800PRO in 256MB (either go for 9800PRO 128MB or 9800XT 256MB), 9800PRO 256MB has showed poor results as compared to 9800PRO 128MB.
and in motherboard, do not buy on nVidia chipset, go with VIA chipset, on models K8V Deluxe, (if you are buying 754 pin version of processor) and MOST RECOMMENDED is that, as now AMD has made both Athlon 64BIT and Athlon FX 53 on same pin design (i.e 939 pins), BEST is to buy Asus A8V Deluxe (on VIA K8T800 Pro chipset), this will help you out in such a way, that in case you decide to upgrade your processor from AMD 64BIT to AMD Athlon FX 53 (whicn is more powerful), then you dont have to change the motherboard as well (as from now, both Procesors have same number of pins).