all you do is put a field and button and point the form to the Site Search page....
if your site is in html, may i just check you have support for ASP?
anyway you can copy this:
<form action="/search.asp" method="get" name="search">
<input type="hidden" name="mode" value="allwords">
<TABLE BORDER="0" CELLSPACING="0" CELLPADDING="0" width="100%">
<TR>
<TD align="center"><input type="text" name="search" maxlength="50" size="10"></TD>
<TD align="center"><input type="submit" name="submit" value="Go!"><br></TD>
</TR>
</TABLE>
</FORM>
you will need to edit this to fit it in with your site, but thats about it
i put a hidden feild into do the "all words / any word" thing, if my users want to change it then can do so after searching 
you dont have to have the code to do the search on every page, just the one you downloaded and point your other pages to it like i did..
hope this helps
also this was the wrong forum..
the correct forum was "Web Wiz Guides Free Applications" i think