I had this issue a year or so ago, albeit with .MXF files. There's several shareware convertors out there (~£20-30) but I wasn't entirely happy with the quality as they massively reduced the bitrate from the source footage (in my case down from 50mbps to 20mbps). There are demos you can try out of you search around, Aiseesoft do one that wasn't bad from the trial I had.
In the end I ended up with Sony Vegas (Pro) which natively read the files, and accelerated rendering through my video card. It also eliminates having to do the intermediate conversions stage which IMO would get to be a pain in the arse with lots of footage if you just want to crack on with editing.