You shouldn't really be including hacks straight into your main css. The main reason being that you have no idea how future browsers will handle the hack because is basically undocumented, and this might cause you - or your client - grief in the future.
Include a new stylesheet via conditional comments and you can isolate any IE browser while not needing any hacks. (i.e., you can just declare the background color directly)
Most clients don't want to pay you to create an IE only CSS file, takes minutes I agree but if they won't pay a few quid extra then why should I do it.
TBH I usually do this sort of thing (add an ie6.css file instead of a hack) as I tend to over-engineer rather than keeping to the agreed spec and work schedule.
Include a new stylesheet via conditional comments and you can isolate any IE browser while not needing any hacks. (i.e., you can just declare the background color directly)