I use Linux Mint 13 (32-bit) as my operating system and have found several RAW converters that work under Linux for the Sigma DP2 Merrill. The software below will work with different versions of Linux flavours and even possibly Mac OS. All will export to TIFF for further manipulation in your favourite image editor.
dcraw (Linux commandline software - the most basic and requires user to be comfortable with a Linux terminal)
http://www.cybercom.net/~dcoffin/dcraw/Ufraw (a graphical program which calls on dcraw. Very fast and intuitive to use. At present, this is the one I use to play with RAW image files)
http://ufraw.sourceforge.net/Darktable
http://www.darktable.org/All three will work with Sigma DP2 Merrill files. I post this because it appears some have found difficulty finding software compatibility with the Sigma RAW image files.
Cheers,
Victor
Canada