I have an SD5, and like you, I have used HD Writer to convert to MPEG2, for standard def conversion, for a couple of years now.
I do use another way, with the original .MTS or .m2ts video files, which allows me to convert to a format that lets me save the footage as anything I need - HD or SD!
I convert to Canopus HQ, which you can do using the freebie AVCHD2HQ converter from Grass Valley. You can find it here:
ダウンロード Canopus AVCHD converter
Just click on the link from the bottom left hand box.
It allows you to convert AVCHD to Canopus HQ, or HDV or MPEG2HD transport stream. Fantastic high quality converter.
You need to be aware though,that the utility only works with the Canopus HQ codec installed. That is easy enough to find as a freeware download - see here for example:
RapidShare: 1-CLICK Web hosting - Easy Filehosting
But I should advise that some folk say that the codec shoudn't really be out there as freeware. You'll have to make your own judgement on that!
I can understand if that is true though -it really is a fabulous converter! You can open the Canopus HQ files in Virtualdub, for example, edit if you need to, and then save in virtually any format you want, if the codec is available from Virtualdub!
Just an alternative suggestion!