<p>I have a project using GWT and it displays data in a table.</p>

<p>I need a Table for GWT that supports:</p>

<ul>
<li>sorting by particular column</li>
<li>scrolling the data, while the header is immobile</li>
<li>filtering rows for data searched in the table</li>
</ul>

<p>The project is being created for internal purpose of the company, so I look for a solution that does not require commercial licensing for such uses.</p>

Here is a table supporting sorting and filtering :
http://code.google.com/p/gwt-advanced-table/
Google itself is working on it. Look at this example in the incubator which supports multi-column sorting and fixed header but unfortunately no filtering :
http://code.google.com/p/google-web-toolkit-incubator/wiki/ScrollTable
Other grids and tables are available in the incubator at this address :
http://code.google.com/docreader/#p=google-web-toolkit-incubator&s=google-web-toolkit-incubator&t=Tables
Ext GWT proposes a very nice table, but it is not free (in your case) :
http://extjs.com/products/gxt/