i like your setup, but go with corsair xms series ram, and get 2 sata 36gb 10,000 rpm hard drives. i would recommend wd raptors. configure them in a raid0 array and that machine will be SMOKIN. your hard drive and ram are the only two bottlenecks in that system, and if you do what i said then they wont be bottlenecks anymore. buy it all from newegg because newegg has excellent prices, excellent shipping, and is just an all-around reputable retailer. you could save a few bucks using another site but it might be a mislabedled product, it might have extra shipping costs, etc. newegg all the way.
edit: and that case is good. dont go with a smaller case, that case is excellent and will have great airflow.
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-Mach Speed X-Caliber PT800DBP Mobo (POS!!)
-Pentium 4 3.0C at stock w/ SP-94 & YS Tech Fan
-Thermaltake 420 Watt Power Supply
-Kingston 512 MB Dual Channel PC3200
-512 MB Kingmax Hardcore PC4000
-GeForceFX 5200 128MB AGP Card | Sound Blaster Audigy2 ZS
-WD Caviar SE 160GB HD 7200 RPM/8 MB/ATA-100
-Nec DVD Burner, 32x16x40 CD-RW, 8x4x12x DVD±RW</font>
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<b>Dell XPS T700r</b>
-PIII 700Mhz | 20GB Maxtor | 384 MB SDRAM | NEC DVD-ROM | 32MB NVIDIA RIVA TNT2 Model64