I need to be able to put a onscreen keyboard on my monitor. Do any of the monitors such as Lilliput or Xenarc come with software to drive such an app or is it all aftermarket?
Nothing to do with the monitor. Monitor only displays stuff. The touchscreen overlay only does a mouse. Nothing proprietary about TS's. So it is all software side. Frontends have OSK's, and then the built in XP one, although it is a tad small for my taste.
OSK = On screen keyboard.
FrontEnd = Application which is touchscreen friendly and encapsulates all your programs such as music player, gps, video player, and web browser but makes them look different. Bigger buttons and such.
I use RR (RoadRunner) because it is free. It is not easy to setup, but once does it is great. Streetdeck is available for purchase from the mp3car store for $200. There are many other pieces of software available, but those are the most popular. Also an entire subforum under "Software" then "Frontends" that has a good list of all available ones.