|This is not really a Windows 7 question, but I'll try my best.|
First you have to find out if the selling company is located in the same country as you are, or if it's an international purchase.
Second you have to find out if your card is valid for (international, see above) on-line purchase. This information should be printed in the agreement you signed (hopefully after reading it) when you got the card. If you don't have it, the card provider should have that information.
Third you have to find out if the selling company has some restrictions about the type of card that are valid. This information is usually found on the page where you enter your card details. If not, the selling company should have that information.