In reading through comments regarding Exchange 2007's lack of 32-bit support and confusion around why Microsoft decided to provide a 32-bit "test" version of Exchange 2007, I thought I'd offer some facts about this version and some possible reasons that Microsoft went 64-bit-only with Exchange 2007.
First, as advertised, the 32-bit version is for testing only. Many people like to test server software in a virtual environment before making the production plunge. Take note that Virtual Server 2005 R2 does not support 64-bit guests virtual machines. Even VMware ESX 3.0 only had experimental support for 64-bit guest operating systems. ESX 3.0.1 now includes full support for 64-bit guests, but this is a recent release. Sure, desktop virtualization packages have supported 64-bit guest OSs for a while now, but the enterprise-variety virtualization offerings are just catching up to this.
In short, had Microsoft opted to skip a 32-bit testing version, they would have locked out anyone who wanted to test the product on older servers -- those that do not support 64-bit. I don't think that releasing a 32-bit unsupported test version was irresponsible and it shouldn't be confusing. It's for testing, runs on just about any hardware you have laying around and is easily available.
Microsoft, Exchange Server 2007, Exchange 32-bit, Exchange 64-bit, Review, Article