does minecraft have some kind of memory issue?
I'm asking cos mine seems to crash after about an hour, with a DOS screen full of comments, but relaunching the .exe makes it all work again for another hour
Where's the dos screen coming from? Oh do you mean the ingame thing with the white background? Make a note of what it says next time (or take a screenie).
Shouldn't be a memory thing I think cos java's supposed to be sandboxed. Minecraft crashes for lots of reasons though so could be just you get a crash every hour or so from statistical chance or something.
Anyway yeah, note down the error. Though java errors can be a bit uselessly generic.