For God's sake, DO NOT use a NAS with SQL Server.  You are asking for nothing but trouble.  Even Microsoft does not recommend it.  I've used Network Appliance NAS and EMC and CLARIION SAN's as well as Raid Arrays, and I'm telling you NAS is bad news.  It was never designed to service Databases and it just does not work.

I think in your case, like a lot of people have already posted, a SAN would be overkill. I have several databases >100 GB and we have them running on multiple RAID arrays with no problem.

My advice, whatever the vendors tell you double and triple check the facts.  NAS and SAN vendors always try to tell you that their product will do this and that but most of the time the Sales guys are talking through their *&#*@ and a lot of the time the concept they are talking about is Oracle based not SQL Server.  Not trying to scare you, but make certain you have all the facts, SANs are not cheap.

Good luck,

Angela