Is there a way to call an external web service from sforce.com? I want to add a custom tab to sales.com. Every time the users click on this tab, I want to fetch data by calling an external web service (that we already have) and display the data.

If this is not supported, what is the preferred way of fetching data from an external datasource? The documentation talks extensively about getting data out of salesforce.com. I could not find much information on making outbound calls from salesforce.com. WILs seem to require creation of web pages outside of salesforce.com.

TIA.