Please try our converters. As you can see in the converters download page (Downloads > Converters > vBulletin), we have converters written for version 3, as well as higher.
I actually recommend to try directly with the converter from 3.7, actually, but in any case: any converter you run, it won't hurt anything, it simply reads the vbulletin database data and *tries* to import it to SMF. So you could try more than one converter.
