Are there .Net 4 features you want to use or is it just that you want to use VS2010?

>Hi,
>
>My customers are using my ASP.NET application on their Intranets. The application runs on .NET 2.0 and is typically installed as site on their web server (usually Server 2008). I want to add some new modules as separate applications (that will have a different DLL) but I would prefer to start doing this in VS 2010 and use .NET 4.0. Therefore, on the same site I would have some .ASPX pages using DLL built in VS 2005 with for .NET 2.0 and other .ASPX pages using another DLL built in VS 2010 for .NET 4.0. Will there be a conflict? Anybody sees possible issue with this? TIA.