man i dont know what happen to my other post but....

a 10g partion is a good amount of space to play with. when u install u will end up cutting up that 10 gig into diffearnt filesystems for bsd. ie one for root one for swap and so forth.

teh size of your remaining windows partion would end up being:

size of harddrive - 10gig= whats left for that windows partition.