Hi,
in windows I am able to use winmerge as the external diff tool for hg using mercurial.ini,etc.
Using some options switch that you can find in web(I think it's a japanese website) Anyway, here for example:

hg winmerge -r1 -r2

will list file(s) change(s) between rev1 and rev2 in winmerge. I can just click which file to diff but for bc3:

hg bcomp -r1 -r2

will make bc3 open a dialog which stated that a temp dir can't be found. The most I can do using bc3 and hg is

 hg bcomp -r1 -r2 myfile.cpp 

which will open diff between rev1 and rev2 of myfile.cpp So,it seems that hg+bc3 can't successfully acknowledge of all files change between revision. Only able to diff 1 file at a time.
Anyone can use bc3 + hg better ?
edit: Problem Solved !
Got the solution from scooter support page. I have to use bcompare instead of bcomp Here's a snippet of my mercurial.ini

[extensions]
hgext.win32text =

;mhd adds
hgext.extdiff = 

;mhd adds for bc
[extdiff]
cmd.bc3 = bcompare
opts.bc3 = /ro

;mhd adds for winmerge
;[extdiff]
;cmd.winmerge = WinMergeU
;opts.winmerge = /r /e /x /ub