Depends what you want to use the Cream or Tartar for!
I'm assuming you mean Cream of Tartar? 
They aren't the same thing. What are you using the meringue powder for? You might be able to omit it without any trouble.
Angie
I'm sorry but this made me laugh. I wasn't sure if you were making cream of potato (tater) soup or icing made with Cream Of Tartar.
And the answer is no. Cream of Tartar is used as leavening to make cakes or cookies rise when combined with baking soda. In egg whites it is used as a stabilizer. Meringue powder is powdered egg whites with gums added to it, but it does also have cream of tartar.
Here is an explanation of Meringue Powder
http://www.wilton.com/yearbook/productinfo/meringue.cfm
Hiya D77,
Cream of Tartar is a by-product of winemaking.
It's used in recipes with egg whites and acts as a stabilizer (you can also use lemon juice for this too). Meringue powder already has the cream of tartar added to it as a stabilizer (that interesting tangy taste).
You only use a minute itty bitty bit in your egg whites when you whip them (like a 1/4 tsp or less).
I wouldn't sub cream of tarter for meringue powder, but if you use meringue powder, you don't need to use c of t, but if you use eggwhites, then it would be a good idea.
You can also make your own baking powder with c of t. It's a combination of baking soda, corn starch and c of t. I don't know right off the top of my head what the proportions are but that's how you can make baking powder.
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