Need help for budget file server

APPROXIMATE PURCHASE DATE: This week BUDGET RANGE: $400

SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: Primarily a file server for movies, pictures, etc.

PARTS NOT REQUIRED: keyboard, mouse, monitor, optical drives

PREFERRED WEBSITE(S) FOR PARTS: newegg.com

PARTS PREFERENCES: Case, power supply, motherboard, CPU, ram, 1 HD

OVERCLOCKING: Yes SLI OR CROSSFIRE: Maybe

MONITOR RESOLUTION: 1680x1050

ADDITIONAL COMMENTS:

Here's my current situation. I have a Dell XPS 400 (Pentium D 3.0 ghz, 4 gb ram, 1 tb and 160 gb HDs) acting as a file server for 4 laptops, a PS3, and a xbox 360. The problems are that the 1tb HD is full, no room for another internal HD, and it can't handle 1080p streams to the ps3 or xbox. While streaming, the CPU is at 100% usage which I believe is causing the slowness in 1080p playback. So my requirements are:

1. Case that allows at least 4-5 HD's.
2. Motherboard that allows CPU/memory upgradeability in 2/3 years. Prefer onboard GPU to save cost (but capable of 1080p playback).
3. Don't really care for RAID, but would be nice for additional performance and backup capability. But currently I'll be backing up to an external HD.
4. Obviously capable of 1080p streaming.