Please help us with a fraud situation

Please help us with a fraud situation

We had some identity thefts situations with our credit cards and Bank
accounts.
People using our credit cards and writing checks against our account.

How can I set up a secure internet system in my home ?

I use a Windows XP - wireless laptop to access the internet I have
in my home.
We use Comcast cable.
We have a WPA secure internet. We use a Netgear Rangemax MIM
and the Comcast modem.
Somehow some people have managed to get both our credit card numbers
and bank account numbers and even driving license number.

I use this internet to access all our bank accounts etc.

Because of the fraud that occurred, we want to make sure that
we have a really secure internet connection.

Since I am not a techie, pls help me with as much detail as possible.

Thanks in advance

Irfan Smith