Two mechanisms are in place to search this site.
The first uses a CGI script and allows you to search based on file names and text that has been added to a "database type" websrch.html. This has been hard to keep up-to-date and is now months old but has the advantage that it can be used to find PDB or JDX files etc.
The second uses a JAVA applet from http://www.babbage.demon.co.uk/java.html but only searches the top page and those directly linked from it and then only searches HTML files.
In this case, enter your search phrase and press the "Search" button. If any matches are found they will be displayed. Double click on a match to jump to that page.