Why does javascript interfere with search engine crawls and what can
be done about it?

Here's an explanation and fix from about.com 
Web Search - SEO 101: A Beginner's Guide to Search Engine
Optimization,
Part 5: JavaScript
http://websearch.about.com/library/weekly/bl-seo101-builde.htm

"...search engines are unable to read java script, navigation systems
built entirely with java script (such as drop-down menus) are neither
read, nor indexed by spiders..."
"...whenever possible, JavaScript should be placed in an external .js
file and simply called from the HTML code."

"Creating an external java script file is quite simple and allows you
to reference the same script from several pages without having to
duplicate the code. Simply save your java script as a text file with a
.js extension on it. To refer to this script from your HTML code,
simply call the file similar to how you would call an include or image
file."

< script src="filename.js" type="javascript" >< /script >

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Clarification of Answer by wlk115-ga on 23 May 2003 17:34 PDT

Judging from the 3 star rating this was not exactly the answer you
were looking for, if you would like more information just add a
clarification or comment explaining what you need and I will be happy
to look in to it further.

Referencing an external JavaScript is indeed better style than using
JavaScript inline (since it only has to be downloaded by clients
requesting it).
It can be done as described above, but there should be no space after
the "<" ("<script" instead of "< script").

However this is not a fix to the problem of search engines not
following certain JavaScript-menu links and so on.

The article cited above also has information on providing spiders with
an alternative route to follow links. Sites using java script
navigation should include a duplicate, textual navigation system at
the bottom of the page.

I didn't want to quote to much of her article for copyright reasons.