The big difference is that Bizspark gives you "production" licenses. The Action Pack licences are restricted to non-production usage only.
We actually use the Action Pack today to get access to the latest VS Pro. But it's "limited to three developers", and the other MSDN software benefits are severely limited compared to MSDN pro (e.g. only certain editions of Windows Server and SQL Server).
We actually use the Action Pack today to get access to the latest VS Pro. But it's "limited to three developers", and the other MSDN software benefits are severely limited compared to MSDN pro (e.g. only certain editions of Windows Server and SQL Server).