You are copying the .VOB files from the DVD to a different drive other that the C drive and changing the ext to mpg right?, Otherwise Vegas will try to edit as if the DVD rom was a drive. Been there, done that Veeery slo and you hear your DVD ROM spining. What are your PC specs? Also if the DVDs were copywrited or are Encrypted with anti piracy, You won’t be editing them Vegas.
You didn’t tell us if Platnum has the abillity to capture from disc. I’d hate to think your only option is to capture analog from the DVD.