Navigate to the Advanced Search Page;
Perform a search to return some search results;
Edit the page (Site Settings | Edit Page);
Edit the Search Core Results WebPart (Edit | Modify Shared WebPart);
Under the Data View Properties click the XSL Editor button;
Select all the XSL and save it somewhere to back up the default XSL;
Clear the content of the editor and enter the following XSL:

Save the changes;

Apply the changes to the Web Part and Click OK;

You will now see that the format of the results has changed. View the source of the page to reveal the raw XML.

This is nothing new, but is very used full to get the Raw XML so you can then open your favorite XSLT editor and generate some nice formatting for your search results.