I haven't touched upon the hardware part. All I would like to know is actual case reports about small offices that were doing their work earlier in doze and later migrated everything to GNU/Linux.
Rony, you may be pleasantly suprised to know that the West Bengal University of Technology (http://www.wbut.ac.in/) uses Free Software (specifically GNU/Linux) exclusively on their computers. This goes to the extent that the Vice-Chancellor had (atleast the last time I met him a few weeks back) only GNU/Linux on his laptop, and no proprietary operating system is allowed to use the university network.
To know more just drop in the ILUG-Cal.org mailing list (http://list.ilug-cal.org/mailman/listinfo/ilug-cal-discuss) and place a query. Some of the ILUG-Cal.org members have been instrumental in this effort, and they will be happy enough to let you in on their secrets. :-)
Cheers, Debarshi