Semantic content: images with alt attributes vs plain text?

One of the big arguments I constantly have about SEO is whether semantic content as images (with appropriate alt text) or simple text values will rank differently.

For example - which is better for SEO?

<h1>header</h1>

Or...

<h1><img src="header.gif" alt="header" /></h1>

...And does the H1 tag actually make a difference?

<p>header</p>

Not surprisingly it's an incredibly difficult subject to find any solution for so here at Code Required we're currently running a simple test to see what happens...

You can see the pages at:
http://www.mycardioworld.com/tests/frank.html
(header as image with alt and title attributes)

http://www.mycardioworld.com/tests/fred.html
(everything as plain text)

and...
http://www.mycardioworld.com/tests/roger.html
("un-semantic" plain text)

We'll be monitoring the situation over the coming weeks on all the major search engines and posting updates here - in the meantime if you would like us to add other versions or have any comments please drop Jon an email.(For example should we do a sIfr version? should we do a version without title attributes on the images? etc).

Page name	Position
	Google	Yahoo	Altavista	Ask	Live/MSN
Frank (H1: image with alt and title)	1	n/a	n/a	n/a	n/a
Fred (H1: as plain text)	2	n/a	n/a	n/a	n/a
Roger (P: as plain text)	n/a	n/a	n/a	n/a	n/a