SQL 2005 Mirroring - Which Version?

We want a highly fault tolerant SQL 2005 solution. Rather than using a cluster we have been told (among other things) that using SQL's mirroring capabilities would be the best answer. One vendor advocates Standard Edition and the other says we need Enterprise Edition.

What we want is a highly fault tolerant solution that will fail over (and back) without user intervention. We will only have less than 10 users and it isn't a very complex database application. We will be using 2 - 1.7ghz single processor servers with 4gb memory and multiple hard drives and an exhisting fault tolerant server as the witness.

Can someone further explain the dangers/benefits to using the 2 versions? Remember the failover has to be automatic.

Thanks