Please help us to help you, Gav:
I've had no difficulty in finding the minimum specs to run Train Simulator 2016
http://www.systemrequirementslab.com/cyri/requirements/train-simulator-2016/12853
but you might need to define 'video stuff' a bit better if we're to be able to understand what type of PC is required.
If it simply means watching streamed video (from Youtube, iPlayer, etc), then any modern PC should be able to handle it easily. If it means some basic editing in, say, Windows Movie Maker, then, again, the system requirements won't be particularly high. However if it refers to using professional level video editing software (such as Lightworks), a top-of-the-range computer will be called for.