This isn't really possible in a reliable way, until style
sheets are more widely supported. At this moment, there are
several browser-specific kludges and tricks available, but
these are not guaranteed to work. 

1) Use a number of   ( ) characters. Netscape and related
browsers do not collapse these, like normal spaces, so this
appears as an indent in these browsers. Other browsers can
display it as one space. 

2) Put a <DD> at the beginning of the line. This is
syntactically invalid, but Netscape works around this by
indenting the line at this ball. Of course, other browsers
will handle this differently, and there is no guarantee that
Netscape will keep doing this. 

3) Use a blank, transparent GIF, using WIDTH and HEIGHT to
indicate the desired whitespace. This is a very ugly
solution, as it only works if you have image loading on,
otherwise you get the "Image" icon at the beginning of the
line. Not all browsers support resizing using these
attributes, and you can only "indent" a certain number of
pixels, not characters. So the amount of "indentation"
varies with the font size used to display your document.