The search button (Ctrl+G) uses the Google engine. Is it possible to link to another search engine if required please?

yes, by adding this line to your prefs.js (or user.js) file:

user_pref("kmeleon.general.searchEngine", "<search url goes here>");

for instance, to search the DICT database, you would use

user_pref("kmeleon.general.searchEngine", "http://www.dict.org/bin/Dict?Form=Dict2&Database=*&Query=";

in the upcoming version, it will be possible to script macros to change this string and call the search box with a single command, so that you could have an entire menus worth of search engines, if you wanted, and choose between them...

And of course, you may also want to change the Ctrl+G accelerator if you don't use Google.

Edit -- Preferences -- Configs -- Accelerators, search for "CTRL G = ID_NAV_SEARCH" and change the "CTRL G".

One very good reason to stick with Google, though - it's good, and it's honest. You get what you're looking for, and not just what somebody paid to stick in your face.
I would make Google my default if it wasn't already. )