Presumably you have location information for each of the points (nodes). MapPoint could take latitude,longitude coordinates, or address information (including a simple city + state/county/whatever).
You are also asking for straight lines which makes it relatively easy to code up. You would load the node data, convert these to location objects.
Perhaps plot a pushpin for each location if required (optional).
Then load the link (flow) information. Then for each link, a line is drawn between the two relevant location objects.
I think MapPoint has only a limited range of line thicknesses, so this should be borne in mind. The link colour can be changed as well, so this could increase the number of combinations available.
Depending how urgent this is, I could be hired to write this for you...
