Disconnections are a scourge of UK ADSL services.
A few pointers - the 2.2Mbps you are referring to is the line speed - ie the potential maximum throughput you can get. That's the maximum you will get in the UK on a standard BT line (I won't go into LLU (local loop unbundling) here, but it's coming to most of us soon, meaning potentially much higher speeds).
My guess it's an issue out of your control, and with BT or your ISP. You've done most of the diagnostic stuff I would recommend. For a general health check on your connection, download Dan Elwell's program
here. It will give a good indication if there are any other issues with your connection, and a bit of armoury to go back to Pipex with if all is not well.
The error messages you are getting in your browser are unlikely to be related to this problem. Try to copy to your clipboard the exact error message and google it - usually works for me! A re-install of IE / OE6 won't remove any of your personal stuff. I'm not sure, but you might get an option to 'repair' your current installation anyway.
Hope this helps.