Movable line via mouse

I in now way need/require anyone to completely solve this issue but need ideas on how this might be accomplished. Situation: I have data on six different sites, and each collect data period has a +/- 30 minute skew for each site. I need to allow users to see these data collection periods for a given day and select when they want to look at data for all six sites. I can solve this problem without using graphics and just displaying text times and having the user enter in the times manually but I would like todo it with graphics. My idea: Generate a timeline in a window, with the sites listed on the left side of the window. Then there will be two vertical lines that a user could click on and drag to the appropriate times they want to start and stop looking at the data. What I know I can do: Generation of the window with the full timeline and placement of data lines for each site in a GtkLayout. What I don't know how to do: Clicking and dragging of the line. The closest thing I could find to this functionally is the colorselector.php demo using GtkColorSelectionDialog. Any help or pointing in the right direction would be helpfull. Mahalo, Tabber Watts