Hey Jakeman,
Mike's right. In addition, you can also use the software that comes with any AVCHD camcorder to peice your files together. Also, QuickTime Pro also joins multiple video files (including MTS with the Perian plugin and the MPEG Component) into a .mov.
As you know, the files lose a few frames of video between each file due to the way MPEG recording works. MPEG Long GOP puts frames into a "Group of Pictures" usually of 12-15 frames each. If your recording medium stops writing a video file before the 12-15 frame group has been made, you could lose the frames it recorded before becoming a group or GOP. However, there is metadata associated with the clip that will instruct smart software how to join the two clips properly without losing any frames. The one Mike mentioned can do it, most software that comes with a camcorder can do it, and if you import your footage straight from the same folder structure it was written to in Adobe Premiere, you can keep these frames too.
Hopefully that helps!
Dan
