I'm not sure if that PSU would support that system, especially if you go dual-core and/or you want to upgrade in the future. Integrated PSU's that come in cases tend to be on the weaker side, so I'd buy a seperate solid Antec or OCZ PSU. I'd definetly agree that $100 is rediculous for a DVD burner, and unless you think your going to be doing alot of DVD burning, I'd go with a solid but cheap CD burning DVD reading drive, because when blue ray drives hit the street, you'll probably want one ... and HD DVD probably.
Go with a Sata 150 HD, ata is being phased out.
I don't know what you'll be doing with the computer, but unless your running games, simulators or other graphic intensive things, I doubt you need the 7800GT.
As others have suggested, I'd go dual-core, but the 3700+ is very solid and can be OC'd to 4000+ speeds and beyound.
Your motherboard is decent, nothing special but nothing horrible either.
Overall nice rig, but I'd really keep AMD's new socket, Socket AM2 in mind, which will be released before the end of Q2 of this year.