I once had a big fat bumble bee in my house, it looked like the normal fat ones but slightly longer and fatter than normal.

I am guessing this was a pregnant queen bee, but I could be wrong, does anyone have any ideas?

There are a few different species of bumble bees. It could be that some are larger (and rarer) than others and it was one of these that you saw.

Probably is a queen. It'll be looking for somewhere to hibernate for the winter. The workers [i]should[/I have all died off by now, but then again, its been such a wierd, warm autumn.
I suspect that inside a house will be too warm for it to hibenate properly, though I expect you shooed it outside anyway - I know I would

She was trying to get out the window, so I opened it and she flew out and away.

Last year my wife found a bee of this size and squashed it I had to dispose of it.

Just get a bumble bee house or similar from the RSPB and put it in your garden.