The Mobo, CPU, and RAM look alright. We could debate AMD vs. Intel, single vs. dual core, etc., but what you have looks fine. Although I have never used that specific mobo model, I have built numerous systems with Asus mobos and they have never failed me once.
The 74GB Raptor is a good idea for the OS drive, and a good idea for your sample streaming drive if you're going to be using a lot of soft sampler instruments, but you're still gonna need a lot of storage for projects, samples, etc. I'd recommend adding another HD with a lot of space (~400 GB). I would also forget about a RAID array as IME it's not worth the trouble. So, you would have an OS drive (74GB), an audio drive (74GB Raptor where projects get recorded to, and possibly some sample are streamed from), and a storage drive (~400 GB for project, sample, music, etc. storage). You could probably make those 36GB Raptors as well.
It looks like the PSU is a generic one that comes with the case. I would recommend investing in a high quality PSU, especially if you are considering adding DAW cards (i.e. UAD-1, Powercore) and will have multiple HDs and DVDROMs in your computer. Look for PSUs that have constant and high amperage rails (i.e. 30A+ on the 12V rail). Since most high quality PSUs don't come with a case, this means you'll have to look for another case too.
Unless you're going to be playing demanding games on your computer (games like Quake 4 or Half Life 2), that video card is complete overkill for a DAW - and I mean COMPLETE overkill. Get a Matrox P650 or P750 and you'll have what you need to run dual DVI monitors.
The Dell 2405W is a great monitor, I have one myself. I waited for one of Dells deals and got mine for ~$850. My Dad wanted to check it out, and after I showed it to him, the next day he called up Dell to get one - this was after their "deal" had expired. Well . . . he got his for ~$810 (he just had to show me up, the bastid
). Anyway, that monitor does not cost $1100 - call up Dell directly and negotiate with whoever is on the other end. If they don't go low enough, just say "no thanks", then call them right back - you'll get a different person everytime, and you just have to find one that will give you the best deal. I wouldn't be surprised if you could get it for below $800 . . .
Lastly, what about HSF and thermal paste? Might want to think about a non-stock cooling solution.
Anyway, with the money you save on the monitor and video card, I would pick up a storage HD, high quality PSU, non-stock cooling solution, and probably some components to make it all a little more quiet (like silent fans, or an acoustipak).
Good luck!