Image magick does conversions very nicely, but
AFAICT it won't handle combining multiple tiffs into
a
single document.
Doc
Actually, it does this very well:
To convert a bunch of TIFF files to a single PDF, try
the '-adjoing' option to the imagemagick utility
"convert":
convert -geometry 1600x1200 -colors 32 -colorspace yuv
-adjoin *.tiff
Similar for jpegs, etc.
Dave