we need to be able to print directly from a browser to a small receipt printer connected locally to the PC that the browser is running on (without the user having to print from the browser manually). Obviously we want a thin solution - so outside of using an applet are there any other viable options?
From a java application yes, from an internet browser, not without a writing an applet. I'd recommend contacting the manufacturer of the printer for driver information, you'll need some kind of driver (windows or otherwise) to connect. If they don't have a DOS/Linux driver, it might be difficult to print without using a windows driver.