well ok lets see here...
1. you want nvida, but you'll only be running a single video card. so you don't need the NF4 SLI, which leaves you with the NF4 and the NF4 ultra. the ultra is the same as the NF4-SLI but it has the SLI mode physically disabled. the NF4-SLI and the NF4-Ultra are better than the plain old NF4.
2. your hard drive may be a bottleneck, but not because of it's transfer interface. like i said earlier the drive itself never reaches speeds that the interface allows. i would still recommend SATA over IDE, but SATA150 is fine.
3. again like i said earlier, the DDR400 is supported by the memory controller on the CPU itself, not the motherboard chipset. so in that respect, the mobo or chipset doesn't matter.
based on info that you've given, I would recommend a mobo from Abit, ASUS, DFI, or epox with the NF4-Ultra chipset. brands like ASRock or Biostar are ok mid-range boards but don't expect superior craftsmenship or quality control. and whatever you do, stay away from PC Chips and ECS branded mobos.
personally, I just bought the
ABIT KN8-Ultra . It has the NF4 ultra chipset and I have always liked Abits boards. and you can't beat the price! I just ordered it last night to replace my ASRock 939Dual-SATAII which worked great but I accidentally drilled a hole into it during a late night hasty mod
I should get it tommorow so I'll let you know how it works. it's not top of the line, but Abit makes good boards and it's only $80.