scrollTop sort of does what I want, except as far as I can tell it’s pixel level, and I want something that operates on a line level. What also complicates things is that, afaik once again, it’s not possible to make textareas not line-wrap.
You can stop wrapping with the wrap attribute. It is not part of HTML 4, but most browsers support it.
You can compute the height of a line by dividing the height of the area by its number of rows.
Tested OK in FF3 and IE6.