Actually, you don't convert to those resolutions but instead filter the conversions in the same manner you would sharpen/correct a photograph on the screen (in real time, which is why there's a heavy processor demand on the upconversion). It's more accurate to say you're digitally filtering the image so correct the problems of converting a 720x480i source to 1920x1080p output. The i->p conversion is the weakness of PCs relative to an STB depending on the source it's mastered from (films are progressive, television is interlaced source). So, to answer the question, the film resolution will never be better than 720x480i but it can be tweaked to give the appearance of higher resolution when displayed and 1920x1080.
EDIT: Sorry to bump an old thread, was just looking for my rapidly dropping tech support request thread .