I looked fairly extensively for this a few months back, and couldn't find anything. Bought one package, downloaded trial versions of a couple of others. Found them all very difficult to use, non-intuitive, full of bugs, impossible to do quite simple things. Gave up in the end.
It takes a while to get used to, but at least it's properly put together. It's more for quick sketches, and you certainly won't produce plans from it, but it might suit for what you want.
My guess is that the market price (low) and support requirements (high) mean that any software vendor capable of producing anything worthwhile simply won't do it for the home market. The professional stuff that can do the job is too expensive and requires too much learning.
If anyone can prove me wrong on this, I'd be delighted!
AutoCad Lite I think is what the cheap version of AutoCad is called -- the package used by a lot of architects. The bonus is that when you have the project designed, you can give the disk to anyone with AutoCad to read it or print off full size plans etc.
AutoCad takes a bit of getting used to, but persistence wil pay off.