It's a good idea to use SignalR.
You can re-build it to .NET 3.5. It will need some labor. You can build it for .NET v.4.0, which would not require you to use Visual Studio 2010. In project properties, you can change target framework to v.3.5 and rebuild it.
Alternatively, you can down-grade all projects to v.3.5 (Visual Studio 2008). On CodeProject, you will be able to find the down-grade tool which would do it for the whole solution or a set of projects. Please see:
SolutionConverter[
^].
However, using ASP.NET hosting supporting .NET newer than v.3.5 would be much better and faster. If you have the existing code for v.3.5, upgrading it to 4.0 or newer version won't be difficult at all and can be done automatically.
—SA