tedster - 4:43 pm on May 31, 2011 (gmt 0)
For now iframes still work that way. However, Matt Cutts mentioned a few months ago in a video that this may change in some situations at least.
So it's not the way I would go. Instead I would look at the coding for the entire page. If your visitors are making much use of the text link, maybe it shouldn't be where it currently is, you know?
Can you add text link to the thumbnail so that both image and text appear in a single anchor element? Does the image have an appropriate alt attribute?