[quote name='Commander0Zero']say I have the original version (non-steam) can I buy the two expansions off steam?[/QUOTE]
If you're in the US region, buying both expansions ends up costing the same as just buying the complete package anyway, so you might as well do that and get the extra cd key to give to a friend.
But yes, they're standalone, and furthermore Company of Heroes is setup in such a way that each of the 3 standalone games includes all the content of the others, it's just a matter of which CD Keys you have that control what gets unlocked. In fact, Steam sticks everything in one folder even if you have all three games, and runs the same .exe no matter which game you choose off your Steam list. Having Steam "download" either of the expansions once COH is downloaded only takes seconds.
So if you buy either or both of the expansions, you'll be able to type in your original's CD key / use your old Relic Online account, and basically have a Steam copy of the original too. Though I think Company of Heroes shows up as a locked "preload complete" title in your steam list if you buy the expansions without buying it, if that would bother you.
You'll also be able to download the gigabytes and gigabytes of patches for your original COH and then use the keys off steam to play the expansions on your boxed copy, if you don't like steam. Though this is a game that really does away with the differences between Steam and a retail copy, since you have to login to a Relic Online account to play anyway.