>>>In Windows 98, I could search for files that contained a certain text, and all worked well. Windows XP, on the other hand, has failed me several times - it is quite clear that not all files are shown.
>>>
>>>Is there a setting I overlooked? or perhaps, can someone recommend a free third-party utility that does work?
>>
>>See http://www.jsifaq.com/SUBM/tip6200/rh6222.htm
>
>So THAT is the mystery - the files not found are not registered.
>
>Thanks a lot - it seems that this will solve my problem.

It was quite stupid decigion on MS part to exclude files from the search if they weren't registered. Unfortunatelly, it isn't the first or the last one.