i recommend an intel chipset like 945, 965 or 975..the brand is really not a matter ...in my experience you`ll only have to pay more for a branded mobo like gigabyte, asus, msi etc.....asrock is doing a very good job
i have a few hints ... now depending of how much money do you have....
gigabyte seems to be doing a good job when integrating intel chipsets...
ga-8i945p,l,g,pg, ge-rh looks cheap and very reliable...
as for oc-ing they are ok.....msi does a better job when cames to oc-ing...
my favourite gigabyte setting is top performance..it ensures you better mem timings and stability.....
now it all cames down to mem modules ..i recommend to you a low timing module ...ddr2 has higher bandwith ..arround 2,5 or 3 gbps dual channel of course.....ddr has only arround 2 gbps also dual channel so...i think ddr2 is the way...and pci-e ....there is no point of going back to old agp set no matter how long you plan to keep your new sistem...
good luck and came back with details