Well... seeing as you said computer, that doesnt include a monitor, so technically you wouldnt need one.. however you included one, so I will show a list below of similar items (all from newegg, i dont have time to check 5 sites, that will outperform pretty much all other possibilities...)
MSI X58 Platinum LGA 1366 Intel X58 ATX Intel Motherboard - Retail - $220.99
Crucial 3GB (3 x 1GB) 240-Pin DDR3 SDRAM DDR3 1066 (PC3 8500) Triple Channel Kit Desktop Memory - Retail - $95.99
Intel Core i7 920 2.66GHz 4 x 256KB L2 Cache 8MB L3 Cache LGA 1366 Quad-Core Processor - Retail - $299.99
Palit AE=4870S+0552 Radeon HD 4870 512MB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail - $264.99
SAMSUNG Spinpoint F1 HD502lJ 500GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive - OEM - $64.99
Antec Nine Hundred Black Steel ATX Mid Tower Computer Case - Retail - $109.99
Creative Sound Blaster SB0570 Audigy SE 7.1 Channels 24-bit 96KHz PCI Interface Sound Card - OEM - $27.99
ASUS Black 18X DVD-ROM 48X CD-ROM SATA DVD-ROM Drive Model DVD-E818A3T - Retail - $22.99
SILVERSTONE ZEUS SST-ST65ZF 650W ATX 12V 2.0 & EPS 12V SLI Certified CrossFire Ready Active PFC Power Supply - Retail - $69.99
BELKIN F5D5000 10/ 100Mbps PCI Desktop Network Card 1 x RJ45 - Retail - $11,99
Ubuntu - Linux for human beings - $0
Total - $1186.90
I suppose they may say you need a monitor, but it ISNT a necessary componant and it will work fine... infact, I seriously doubt ANYONE in your class could beat the build.
Its based around the i920, QUAD CORE at 2.66 GHz, this core only came out at the weekend and destroys all other benchmarks, it is coupled with 3gb of good RAM (although, it is admittadly, not the best available) The GPU is a 4870 (which is a gaming beast, the network card is standard, the PSU is cheap and the HDD is a proven speed freak. The PSU is also a solid buy. The ODD is pretty standard...
Honestly, you wouldnt be able to beat these componants..
But anyway, ill discuss your build...
Firstly, for a $1200 build the RAM is slow, the CPU should be intel, they are faster and OC better.
The seagate isnt as fast as the SAMSUNG equiviliant (the spinpoints are animals that are pretty much equal to velociraptors)
The DVD drive isnt anything special (but it doesnt need to be.., although it isnt a RW, which menas you cant write with it. (neither was my choice.. but thats up to you.) Also it is IDE and not SATA (So worse..)
Not much more to say..o and there is no tower... which i used an Antec Nine hundred for (highly recommended for its cooling). No OS either, i used Ubuntu, any Linux OS wold work, but windows costs money, and to get the i7 CPU you need to take away in other areas.
But the build I suggested is better.. however yes yours would work ^^
Above guy.. the PSU can never have to much power, unless you go for uber overkill, it allows fluctuation without to little ampage on any line. Also your comment on HDD's is crap...its not true... simple.. veloci's are rip-offs and small HDD's get used like dirt..