From what I've seen, in my own personal experience, the bulk of what ZoomText can do is give consistent magnification for the entire screen. This is nothing like K Magnifier, since it only zooms the screen in one small area, making it impractical for daily use. However, you can accomplish much the same thing as ZoomText with a built-in feature of X. Namely that of Virtual Resolutions.
If you have multiple resolutions defined in XF86Config, you can use Ctrl+Alt+(+/-) to change the screen resolution while the screen elements are still drawn at the original highest resolution. So, for higher magnification, you need only define a higher resolution in XF86Config. You can additionally then change your system font sizes, icon sizes, and themes (i.e switching to a High Contrast theme for colors, icons, etc.) through your WM/DE config utilities.
Another feature in ZoomText that may be helpful is text-to-voice. For this, you can use Festival (
http://www.cstr.ed.ac.uk/projects/festival/). Unfortunately, it's not the easiest program to configure, and there's not many programs that use it (Gaim is one, with its festival plugin). I mainly use Festival for piping "echo" into it (with the "festival --tts" option) to make it say random things on the fly for my own amusement :-D.
With a combination of the built-in features of X, some High Contrast themes, a custom large cursor mouse theme, and so forth, you can accomplish much of the same thing as ZoomText, without any additional software. This is really the best solution, afaik, for GNU/Linux at this point. For more information, in general, on the state of accessibility solutions, KDE and GNOME both have accessibility projects here:
KDE -
http://accessibility.kde.org/
GNOME -
http://developer.gnome.org/projects/gap/
