Yes powerfailure is a killer when rendering direct to AVI from bryce - (I cant figure out why they haven't made  the possibility to stop and resume rendering to AVI's and for the matter rendering to disk - some old old old programs like Vista Pro 4 has that abillity)

Regarding freeware that can combine sequences of images i can recomend VirtualDubMod - im not absolutely sure that it can take BMP's - but many programs can batch-process converting of BMP's to JPG's - furthermore it can recompress to almost any given codec (that is if you have the codec installed of cause) - in my experience DivX and XviD codecs with a datarate of 2000 is almost as good as DVD quality

And yes ...have fun