A 400D is hardly an upgrade from an A200.
The A100 and A200 were the first DSLRs that Sony made, they were very similar but models after that got a lot better. When I upgraded from A100 to A350 there was a massive improvement in specs, low light handling in particular was better, 14.2mp sensor, live view (with pull out screen).
To make it worthwhile you moving from a Sony A200 to a Canon model, you'll have to move to at least a 450D, otherwise it's not worth it. And to do that you need to add some more money.
Is it really your Sony camera that's the problem? Do you need to spend more time getting the most out of it?
The only way to really know if it's the camera that's the problem is to try another camera.
Try to borrow a Canon from someone and give it a go for a weekend.
I borrowed a Nikon D60 a while ago, and just didn't get on with it, hated the menu system and the fact that most of the functions I wanted were burried. Really liked my Sony after trying that.
I would say there are 2 choices,
1) sell everything, add some extra cash and go for a Canon 450D kit with at least a 50mm prime as well
2) sell your Sony A200 body and kit lens, use that money to upgrade to a better Sony body (A350 or better)
As most decent photographers will tell you, it's not about having one brand of camera or another, it's about knowing what to do with what you've got whether it's a £100 point and shoot or a £1000 DSLR and about composing the shot properly.
If you can compose the shot, then you can get a good photo no matter what camera is in your hand.
