I'm building a pc for my cousin and I need help picking the parts. It will not be a gaming pc, but might be upgraded later for light gaming. This is what I have in my cart right now. I need suggestions on better options for the price (another part that is comparable in price and is better) or any suggestions to cut down on the cost. I also need someone to check if all the parts are compatible. It looks like they are. There's no case yet. I'm not sure how to pick one. Any recommendations?

Motherboard ASUS M4A78 Plus AM3/AM2+/AM2 AMD 770 ATX AMD Motherboard - Retail

CPU AMD Athlon 64 X2 6000+ Windsor 3.0GHz Socket AM2 125W Dual-Core Processor Model ADX6000CZBOX - Retail

RAM G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory Model F2-8500CL6D-4GBNQ - Retail

PSU CORSAIR CMPSU-450VX 450W ATX12V V2.2 80 PLUS Certified Active PFC Compatible with Core i7 Power Supply - Retail

HDD Western Digital Caviar Black WD6401AALS 640GB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive - OEM

I know that psu might be overkill, but she might want to add a video card later on. Maybe one that is a little below a 8800 gt.

Feel free to say this build is garbage and come up with your own. lol I'm trying to do the best I can for below $400.

She went to a few stores and the ones she wanted were $700+ including the monitor and the specs were about what I posted.  I've put together 2 gaming PCs so far with help from people on the other gaming board which shall not be named.  I need input on what parts to buy.  The actual putting together of the parts is quite easy.

" woah dude. ur building a pc. cant u just buy a cheap one, what ur doings insane and u sound pretty stressed out. sorry u r waaay out of my league on this one, all i can say is good luck and please post a pic of it when (if) its finished "

I've revised it with some suggestions I've gotten. Does this look good?

Motherboard ASUS M4A78 Plus AM3/AM2+/AM2 AMD 770 ATX AMD Motherboard - Retail

CPU AMD Athlon II X2 245 Regor 2.9GHz Socket AM3 65W Dual-Core Processor Model ADX245OCGQBOX - Retail

RAM G.SKILL 2GB 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Desktop Memory Model F2-6400CL6S-2GBMQ - Retail

PSU CORSAIR CMPSU-450VX 450W ATX12V V2.2 80 PLUS Certified Active PFC Compatible with Core i7 Power Supply - Retail

HDD Western Digital Caviar Blue WD3200AAKS 320GB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive - OEM

Case Antec Three Hundred Black Steel ATX Mid Tower Computer Case - Retail

CD/DVD Sony Optiarc DVD Burner with LightScribe Black SATA Model AD-7241S-0B LightScribe Support - OEM

I'll probably add another stick of 2 gb ram to it later on.   Should I be getting ddr 1066 ram?  It says this on the motherboard.

That build vs. this http://www.costco.com/Browse/Product.aspx?Prodid=11485562&whse=BC&Ne=4000000&eCat=BC|84|56671&N=4035053%204294967277&Mo=4&No=2&Nr=P_CatalogName:BC&cat=78521&Ns=P_Price|1||P_SignDesc1〈=en-US&Sp=C&topnav=

Which one is better? It will come out to be around the same price after adding a monitor. If it's only marginally better, then she should probably just get a store bought one.

It won't let me link to the page... It's this one.
Compaq Presario
AMD Athlon X2 7550 2.5GHz
6-in-1 Card Reader
LightScribe 16x DVD±RW Drive
Windows® Vista Home Premium
Item # 480291

Ok then I will be the one to say go Intel for your CPU. I know for a fact that they perform better than AMD based CPUs price for price. 
 
But whatever you ultimately choose, have fun with your build and good luck! :D

" Ok then I will be the one to say go Intel for your CPU. I know for a fact that they perform better than AMD based CPUs price for price."

 Don't go with the antec three hundred for a tiny bit more the NZXT Beta is a far better case features/performance plus also Crossfire is not recommended for anyone who is not going to be gaming go with a cheaper single pci-e slot alternative and buy some extra ram.