As many can note in the news recently, there are many questions as to
GWB's involvement with Harken Energy and his lack of filing "Intentin
to Sale" forms with the SEC.  Following the demise of Harken's stock
to $1, it later climbed to $8 within a year.  Between 8/21/91 and
8/27/91, their stock price nearly doubled and volume increased by
2000%.

I seem to recall reading reports that Harken had at one point received
funding from Unical Oil or Enron, but have been unable to find any
evidence to this or any news reports with further discussion on the
matter.

So is this true, and where can I find more information about it if it
is?

It may not be totally accurate to say that Enron was an investor in
Harken, but they had close ties at one point.

An alternative news publication called “The Progressive Review” has
covered the Bush family and their business dealings extensively. They
have several articles that can help shed light on your question and
how Harken did business.

http://www.prorev.com/

The first is a timeline called “Behind the Bushes” which highlights
some potentially scandalous moments in the political and business
histories of the Bush family:

http://prorev.com/bush2.htm

A quick search of this document will reveal plenty about the Bush
family, Harken, Enron, Unocal, and much more.

The second is called the “Bush Harken Timeline” which can be found
here:

http://prorev.com/jul3.htm

There was also an article in the New York Times recently that
highlights the most specific connection available so far:

“In his earliest known tie to the Enron Corporation, President Bush,
then an oil man in West Texas, joined an energy drilling venture
organized in 1986 by a subsidiary of Enron. The drilling operation -
which succeeded in striking oil and natural gas in Martin County -
came as Mr. Bush's company, the Spectrum 7 Energy Corporation, was
struggling to stay afloat during a collapse in world oil prices. The
company was also in final negotiations to be taken over by a
Dallas-based company, Harken Energy.”

“Bush Joined Unit of Enron In '86 Venture To Seek Oil,” by Jim
Yardley. The New York Times, (March 6, 2002).

(This article is no longer freely available in the Times archives, but
you can purchase a copy for a small fee. Copying the entire article
here is illegal.)

An article in a publication called the “American Freedom News”
released an article in September 2001 that highlighted some of the
other investors in Harken Energy, many of whom were wealthy Arab and
Saudi businessman with ties to the oil industry. “Abdullah Taha
Bakhsh, the Arab who cosigned the $25 million cash infusion into
George W. Bush’s Harken Energy Corporation, appointed Talat Othman to
manage his 17.6 percent share in Harken Energy Corp.  Othman, a native
Palestinian, is president and CEO of Dearborn Financial Inc. – an
investment firm in Arlington Heights, IL.”

“Bush family’s dirty little secret” by Rick Wiles (September 2001).
American Freedom News.
http://www.americanfreedomnews.com/afn_articles/bushsecrets.htm

While the information contained in this article appears to be correct,
American Freedom News is not a news source I regularly use or know. So
I’m not vouching for them.

Some other sources for more information would be the Dallas Morning
News, a Texas newspaper that has covered the Bush family extensively
for many years, and a politically motivated web site run by democratic
bigwigs called The Daily Enron that seeks to portray Bush badly.

http://www.dallasnews.com/index.html
http://www.thedailyenron.com/

Search terms used:
Bush enron harken energy unocal
Undernews
Investors

It wasn't as specific as I'd hoped, but I have high expectations too. 
He did point me in a very good direction though with plenty sources to
reference as well as summarize the background details.

You can also view a story on the SEC's report on Bush's 1990 dealings,
and the report itself, @ The Public I's site, part of the Center for
Public Integrity, a not-for-profit organization whose mission is "to
provide the American people with the findings of our investigations
and analyses of public service, government accountability and ethics
related issues."
( http://www.public-i.org/dtaweb/index.asp?L1=40&L2=0&L3=0&L4=0&L5=0 )

The article, called "Bush Violated Security Laws
Four Times, SEC Report Says," By Knut Royce, is @ 
 http://www.public-i.org/story_01_100400.htm