How to show pending changes only for the currently opened solution in Visual Studio 2010 (TFS) and not the complete list of all changes?

Open the pending changes window. You can find there a toolbar button that filters on the current solution.

Yes, on the pending changes view one of the last icons along the top is a "filter by solution" (next to the refresh icon). Click that to reduce the change list to the current solution.

You can see a screenshot of it here