are you the same person I've been helping in email to do this with romlister?
I had 2 people in 1 day asking for a method of converting a favorites.ini file to something romlister could work with. If you've not been emailing me (jeff, the author of romlister) then you are in fact the THIRD person in a 48 hour time span to ask about this, and I have never had this question come up in all the years I've been supporting romlister so far. [insert eerie music here]
the good news: it's pretty easy to do, and you don't have to do any of it by hand.
the bad news: it's a few steps and somewhat time consuming.
you have to move all the roms from your favorites.ini list to a new folder (assuming you have a ton of other roms in your roms folder already that are not in your favorites list) then use romlister's rom scan utility to then match your favorite files against the master input xml file. For the folks who contacted me, I converted their favorites.ini into a batch file to do this.
throw me a PM or email (contact info is on the romlister home page) and i'll get you through it.