You can open them in FM11 and then those in 12. I also believe that you can use 10 or maybe 9 also, but I know 11 works. There is a chart for this on the FM site, but I couldn't find it for FM12.
I'm thinking 11 might still be downloadable for a 30 day trial to do this.
can't seem to find an older version to download for a trial to do the conversions....i'm guessing I need 10 or 11
FMP 11 30 day trial http://info.filemaker.com/Us_en_FileMaker_Pro_11_Trial.html