Comparing Cell value of gridview with textbox value

Question

I have a gridview with 6 columns(SAPUserID ,SAPDescription,SAPPassword,OSUserID,OSDescription,OSPassword) and a CHANGE PASSWORD button. After clicking this button the panel (pnlChangePwd) below the grid view becomes visible containing 3 textboxes(User ID, New Password, Confirm Password) and a Save button.At present if i type new password same as old one, it accepts. how to compare the value in txtNewPassword with cell value of SAPPassword or OSPassword in grid view?

Note: at a time only 3 columns are visible depending upon the data user want(SAP or OS )
Please help..