As it should be quite easy to add a parameter in the querystring when you do it eg. in an HTML module (just write them down), I assume you are trying this to achieve this from a module in the code behind to be populated dynamically.
The solution is Response.Redirect(DotNetNuke.Common.Globals.NavigateURL(...)). You have different options, but the one you are looking for is propably one of these two:
Globals.NavigateURL(string controlKey, params string[] additionalParameters)
Globals.NavigateURL(int tabID, string controlKey, params string[] additionalParameters)
In any case, the additionalParameters variable must contain strings, something like name1, value1, name2, value2...
This could be eg (pseudo code)
int forumID = ForumsController.GetForum(thisone);
int threadID = ThreadsController.GetThread(forumID, "Passing Parameters To Pages");
Globals.NavigateURL(String.Empty, new string[] ({ "forumid", Convert.ToString(forumid), "threadid", Convert.ToString(threadID), "scope", "posts" });
to get this page here (just to give you an idea).
Happy DNNing!
Michael