How to add Lead automatically to campaign capurted from Web?
Create Web-to-Lead form under YourName-->setup-->Customize-->Leads-->Web-to-Lead
Then click Create Web-to-Lead form
Include the fields, which you want to add in the web form
Then Click Generate
Now HTML code is generated.
In the HTML code just add these two line
<input type="hidden" id="Campaign_ID" name="Campaign_ID" value="<Specify the salesforce Id of the campaign>" /><br>
<input type="hidden" id="member_status" name="member_status" value="true" /><br>
Now click save and include in your web page
Now we are done.
All the leads captured from the web-to-Lead form are automatically assigned to the campaign which we specified.