First question I'd ask is what tools, environments, languages etc you're familiar with. The second thing are the requirements. Do you need access to local (client side) resources (disks, drivers etc) or programs (Office interop and so on).
Those two should narrow down the possibilities. If no client side interaction is needed (or it's very light) creating a web based application is easier to maintain and to distribute (well, everyone has a web browser
About the environment. As JSOP suggested both Silverlight and ASP.NET are good and simple to use. If you decide to go to desktop application, personally I would choose WPF with ClickOnce distribution (since this was an internal application). If you're not familiar with WPF, it has a learning curve but on the other hand Forms is starting to take it's last breath (again personal opinion).
And then the languages. C# would be my favourite. One good reason is that it's widely adopted so getting help is easy. Also C# isn't that much different from for example VB.NET but the programming power is far greater. Using C++ would perhaps be an overkill if no special requirements exist.
And lastly the database. Most likely I'm going to be flamed because of this but Oracle is more capable and adjustable than SQL Server. But, again the learning curve is higher and getting help with Oracle is a bit more difficult so I would still choose SQL Server.
So perhaps in a nutshell: Select tools you know how to use or that are easy enough to learn and tools that you can get easily help with if questions arise.