Oh yeah, just a couple more more things...
... in favor of buying pre-build... it's already got all the cables, and you know the parts are all compatible. The system will have been tested, it will at least start up after you plug it in.
... your system doesn't have firewire (1394) or any card readers. Most won't notice or care that these are missing, but some will insist on having either or both.
... beware people who make up their own numbers and claim they did research for you. The system you specked out is $1210... $13000 w/ WindowsXP home. Ad about $40-$45 for shipping. I just put together a $1000 system, but couldn't get a great video card or a great CPU. I had to settle for a 6600 and a single core AMD 3200+.
So the price is in the same ball park. The mfr gets a discount on parts by buying in bulk, but has to charge you for their labor. You can save on the labor by doing it yourself, but must pay the standard rate for parts.
And yes Miles, great minds do think alike.