look for one of those Antec Server Cases like seen here:
Also make sure that you get a decent PSU because generics just dont cut it. Invest in a good PSU and your server will last and be stable.
The hardware you put together is quite good (especially on my standards as my servers are generally P3's). What type of tasks are you planning to use it for? SQL database and web serving? If so, how many users? File serving? FTP? How many peak users and load is this server expecting?
Core 2 Duo E6400, DFI Infinity 975X/G, 2x 512mb DDR2 667mhz, Albatron 7900gt, WD 200gb SATA, Samsung DVD-RW, Silverstone ST-50EF 500w PSU.