That gives you the previously build step. To retrieve the status of a specific step, use
Project.Steps(vbldStepMain)(<0-based index>).BuildStatus
if you know its position. If you know its name (make sure it's unique for that step collection), use
Project.FindStep("step name", vbldStepMain)
to determine its index. When calling script expressions from a step property, remember to surround it in [brackets] to tell VBP that it's script.
http://visualbuild.com/Manual/?buildstatusproperty.htm
http://visualbuild.com/Manual/?stepsproperty.htm
http://visualbuild.com/Manual/?findstepmethod.htm
http://visualbuild.com/Manual/?stepitemproperty.htm