in most cases, a taught masters last one academic year, whereas a research masters often (but not always) lasts one whole year, ie. sept-sept. in a taught course, the vast majority of the course will consist of taught lectures/practicals etc, with maybe a short project at the end which may last a couple of months. a research masters is generally a few months of taught lectures, and then a large project (in my case it was 6 months lectures followed by a 6 month project, but this may differ subject to subject). in general, a research masters is geared more towards students who wish to continue onto more research such as a phd, but that doesn't necessarily mean they are a better choice! if you are deciding between a taught and a research, i would go for the one that is most relevant to you and what you intend to do in the future rather than worry too much about what type of masters it is. generally, a masters is a masters and as long as you get a good grade it shouldn't matter to a potential supervisor/employer which type you did, as long as the skills/knowledge you acquired is relevant.
hope this helps, any more questions then just ask! :-)