Are you going down the route of each developer will have their own machine which have Hyper-V with a load of VM's SQL Visual Studio etc, or will it be one Hyper-V server with VMs SQL Visual Studio etc for 100 developers?

If its the first then if each developer has an MSDN licence issued from your company then as long as you use the software in a development environment and use software downloaded from MSDN only then there isnt any costs.

Be aware that MSDN Ultimate per user is around £5000 (last time I purchased one) so could get very costly.

If its the latter with only one Hyper-V box then from what I understand, if the Hyper-V server is assigned to a user and that user has a MSDN licence then your good as well. In terms of assigning it doenst mean that the person has to look after it etc, just that the server is linked to MSDN licence which is linked to a user.

If the cost of all this is too great, look at purchasing the individual components, Windows Server Data Center for unlimited VM's, SQL Developer edition, Visual Studio 2010 Ultimate and any other software needed and see which is going to be the cheaper option.

Not touched licensing for a few months so things may have changed