A 400W PSU is going to be a lot more than is even needed. Even though it is likely a no name PSU, it supplies way more than enough power, and should be ok. Not everyone needs an OCZ Modstream...
Also, for the motherboard, I would recommend the Gigabyte GA-K8NS-Ultra. I own said motherboard, and I have had nothing but good experiences with it. It is stable, has good features, and is relatively inexpensive. It also features the NForce3 chipset, which allows skt939 CPUs and has an AGP slot.
Also, another couple things to look for:
-Make sure the Hard Drive is a good brand name (Seagate or Western Digital) and is 7200rpm with 8MB cache.
-Get a 9800 Pro with 128MB of memory instead of 256MB. The 128MB performs better and is cheaper. But, if you can afford it, get a 6600GT. It will last a bit longer and performs quite a bit better than the 9800 Pro. I cant knock the 9800 Pro, though. I own one, and it performs quite well.
Other than that you should be ok. If you decide to go with that system in your first post, you should be able to run any game out right now.
Intel E6750...........PSN: ELBATROP
XFX nForce 650i Ultra
Patriot PC2-6400 8GB (4x2GB)
36GB WD Raptor
Samsung SyncMaster 931c
Samsung SyncMaster 750s
Windows 7 Home Premium 64