I stumbled on this while looking for a replacement windows calculator because, the new one sucks of course..
It's called TiEmu and it's a TI graphing calculator emulator.
I just got my TI-89 working and I think it's awesome. You could have full screen TI-89!
It's a bit confusing on the installation, but once it's up and running, it's worth it.
You can use a picture of your TI calculator, or simply calculator's screen that fits your whole monitor.
Here is the link, and don't forget to download the GTK run time package at the top of the page
before running the latest 3.03 version, as the one that the program tries to automatically download, does not work.
Here you guys go, hope you like it:
http://lpg.ticalc.org/prj_tiemu/