If you're set on internally hosting your mail archive, the Barracuda box isn't bad at all. We use it at the new company and it holds up quite well.
Alternatively, I believe the new version of exchange supports archiving natively. This could be a catalyst to upgrade to the new version.
http://www.microsoft.com/exchange/en-us/email-archiving-and-retention.aspx
However, why host your own? The cost and hassle can make it not worth it. Hosted solutions are great. My old company used to use evault, which was a nightmare and a half. We then switched over to Smarsh and never had any complaints. They just worked.
So Make sure you do a cost/benefit of all your options, you might be surprised at what you find suits you.
