Q) Can you confirm how I should license my SQL Server software if my users aren’t actually accessing the server directly? The users will be accessing an internally developed application which will in turn be accessing the SQL Server software.
A) The scenario you describe would be considered multiplexing under the terms of your licence agreement(s). In most cases, you need a Client Access Licence (CAL) for every device or user that accesses or uses the services of SQL Server 2005. This is still the case, even if a user or device is accessing the software via an intermediate product.
Q) If we buy the Microsoft Windows Vista Upgrade under our Volume Licensing agreement, can we then run either the 32bit or the 64bit edition of the product? Or is there a separate licence for the 64bit edition?
Yes, this licence allows you to run either version without the need to buy any extra licences.
Q) I am currently running a pre-installed (OEM) version of Microsoft Windows Server 2003 Standard Edition. I would like to run a virtual instance of the server on top of this to host a particular application we use. Can you advise if I need to buy any other licences to do this?
In this case you would need to buy a further Windows Server licence. You can get more information on licensing virtual instances of Windows Server 2003 here.
Q) If I buy Microsoft Windows Server 2008 Datacenter Edition, do I still need to buy Client Access Licences (CALs) for all of the users/devices that will be accessing this product?
Windows Server Datacenter Edition is licensed under the Per Processor and CAL model. Every processor in the box needs a processor licence, and every device/user accessing the services of the Datacenter server needs to have a CAL. Once fully licensed, Datacenter edition provides unlimited virtual Operating System rights
For more information, visit Licensing Windows Server 2008 Datacenter Edition