Hi blindfoldjump, trying to collapse an edge is very much a polygon modeling concept  MoI is based off of a very different workflow than that. With MoI you are usually working more with curves to define shapes, both for constructing base forms and also using other profile curves as cutting objects in boolean operations.
With NURBS modeling it's more usual to create something like a triangular box by extruding a triangle to start with, and not on starting out with a box and then pushing vertices of the box around to morph it into a different shape.
If you did want to start with a box with NURBS modeling they main way to change it is by cutting the box with some boolean operations, so you could do something like position a cutting line that divided the box into 2 pieces from a side view, and then use boolean difference to cut the box with that 2d profile curve to leave a triangular end result. You don't really form things by the type of point and edge manipulations that you're used to with Modo.
You might want to check out some of these tips for people coming from a poly modeling background:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2
Also check out the tutorial videos here: http://moi3d.com/3.0/docs/tutorials.htm  these videos show the basic profile curve driven workflow that MoI is based on, if you watch those you'll see some simple objects constructed and how the main tools used are drawing curves and doing boolean operations, not by pushing polygon cage points or edges around.
In a NURBS model edges are often times not just straight lines even, edges can be bendy spline curves that are the generated from the intersection between larger spline surfaces. So even the way that models are structured is very different with a NURBS model versus a polygon mesh model. It's more typical to treat surfaces in NURBS modeling more as large sheets of material that you can then cut portions out from, not as a lot of little individual small elements like polygon faces.
 Michael
