I have BES 4.05.6 installed on Windows 2003 for SBS/Exchange 2003
connectivity. I could not view attachments on the handhelds. They
appeared to be coming through, but when I tried to open them, I would
get an error stating that the attachment server was unavailable. I ran
a test from the Blackberry Manager console, and it said that the
attachment service was not running. I checked it in Computer
Management, and it was running. I restarted the service, tested again,
and got the same result.

I have seen another post that mentioned re-registering some DLLs, and I have done the same, but I still can't view attachments. Any suggestions, besides a complete reinstallation?

Check the bes server config to ensure that it points the bes to your local attachment service. Hostname should be "localhost" - the default configuration. If its anything different like a host name or IP address, then someone has changed it.