Add reference to System.Data to a class

Question

Hi,

We have an asp.net application(1.1) written in C#. Application has around 25 forms.
Looks like when the previous developers developed application, they did not design it to be
multi tiered. So they use data connections when ever required. I created some functionality
in a web page. New requirement also needs similar coding. So instead of repeating code in both the pages, I decided to add class and put common functionality there and retrieve it into individual pages. So I added class from project->add class. It added class. It has only System name space.
I tried to add the code like:

using System.Data

but intellisense doesn't show Data when I give dot next to System.

What is the problem. I get it in codebehind file like availablebalance.aspx.cs and System.Data reference is added to project automatically when project is started.
I would appreciate your response.

Thanks,
chinnamma