is there a way to convert vbulletin to mybb directly?
Not publicly, but the
MyBB Merge System is currently undergoing Beta Testing, so there will be a way soon enough.
We are testing the new merge tool that will allow you to merge any other BB software with MyBB.
A unofficial VB 3.5 converter is under development also.
Look
here
The MyBB Team work on that will come out as soon as they done.