Sorry its taken me so long to get back, my Internet connection has been down.
IIS is not the issue, IIS can fly on just about any box you can buy new today. The issue is the application.
Well 100 users is really not that many. In fact based on what this appliation is doing, I would say the most important part is that you have plenty of network bandwidth between the users and the IIS server and the IIS server and DB server. It sounds like you have a lot of data transfer with very little processing.
So I would go with at least 32GB of RAM and either a single quad-core CPU or two dual-core CPU's. If you go with a single quad-core I would go with a box where you can add a second CPU later on just in case.
The amount of disk space should not matter than much, as nothing should really be stored on that server for any amount of time.
Now to answer you question on why you can't get a simple answer. Part of the problem is you perceive that your question is simple, when it is not. There are way too many factors to take into account.
Take the question: "What is the best vehicle I can get to take me from Washington D.C. to Los Angeles, CA in the least amount of time?" Sounds simple right? Well its not. Because the question does not state other factors such as the number of people or amount of cargo. If it was just me, there would be one answer, if I need to get 400 people there, it would be a different answer and if I needed to transport 10,000 tons of cargo yet another answer.
If you were running IIS to serve up static web pages, or do simple queries and support 10 users any desktop today would be able to make IIS fly. However if you are doing complex statistical analysis and trying to support 10,000 users, well that would take a BIG server, actually it would take a farm of servers.
Don't take this personally, but the fact that you don't seem to understand this concept indicates that you may be in over your head.
