Import|convert AVCHD to iMovie

Have a look at Movie Converter for Mac
Movie converter for Mac is a versatile 2-in-1 application that integrates DVD ripper and video converter into a single interface. With DVD ripper you can rip and convert DVD content to various video formats smoothly. And with video convert you can convert between almost all video formats include SD formats like AVI, WMV, MPEG-4 (MP4), MPEG-2, DV, MOV, VOB, MKV, FLV, 3GP, RM etc and HD formats like AVCHD (mts, m2ts etc), MOD, HDV, HD MP4, HD AVI, HD WMV, HD MOV etc so you can import into iMovie (no need to consider iMovie version) or put on various portable devices and applications.

Mac movie converter is also an excellent editing tool that has been enhanced to run on both PowerPC and Intel (Snow Leopard included). With it, you can edit your AVCHD (mts, m2ts etc) files freely. If you want to cut your videos to a certain length, no problem, by dragging the first slider to set the start time and the second to set the end time, you can easily achieve it by Trim function, adjust the aspect ratio by Crop function, or apply special effect to your files by Effect function. Besides, the merge function and built-in batch processing function are also available.

http://www.dvd-to-imovie.com/tutorials/34-import-convert-avchd-to-imovie.html