OK, I seem to have got there at last.
I’m using a 64bit system and the method described by joohansson didn’t seem to work. The K-lite Codec package was all 32 bit codecs and none of then showed up in Pointools, there was a K-lite 64 bit package but that didn’t include a 64 bit version of the x264 codec.
In the end I downloaded the Xvid codec mentioned here: viewtopic.php?f=76&t=3439#p14151
. I tried rendering to jpegs then using Adobe Premier Pro CS5 but the file sizes went silly again. In the end I just rendered straight to avi with the Xvid codec in pointools. This produced beautiful HD videos at very manageable file sizes. I am very happy with the results.
On an aside I really like the free avi converter mentioned on the thread, it seem to work much better than Adobe Media Encoder which I had been using up to now.