phranque - 5:03 am on Oct 25, 2010 (gmt 0)

describing the page being linked to

in general, the description of the referenced page should be in The Title Attribute [webmasterworld.com] of the anchor tag.
you want to avoid stuttering and there are a lot of variations on this which are best described in these Accessibility Guideline Techniques:

H2: Combining adjacent image and text links for the same resource:
http://www.w3.org/TR/WCAG20-TECHS/H2.html [w3.org]

H30: Providing link text that describes the purpose of a link for anchor elements:
http://www.w3.org/TR/WCAG20-TECHS/H30.html [w3.org]

H33: Supplementing link text with the title attribute:
http://www.w3.org/TR/WCAG20-TECHS/H33.html [w3.org]

testing with a lynx browser will give you a good indication of your success or failure using these techniques.

many relevant issues were discussed in this thread.
accessibility and <h1> header images:
http://www.webmasterworld.com/accessibility_usability/3844966.htm [webmasterworld.com]

in my experience the alt text in the header images was indexed but i didn't set up a scientific test to compare the effectiveness of pure text vs alt text.
in my case i had to implement an image-based solution and wanted to get the best possible results under the circumstances.