No � You aren�t stuck with it; BT have stuck you with it because BT and Yahoo are merged ;-)
To take the BT Yahoo combined browser and Yahoo Messenger from your system:
Go to Add Delete. Remove Yahoo Messenger and anything associated with it (you will find BT associated with Yahoo Messenger; it doesn�t matter, delete everything that is associated with BT Yahoo Messenger in Add Delete.) When you have cleared down, go to yahoo.messenger.com download page and select either USA or UK version (you have a choice) and download. BT Yahoo will now be off your system and you can carry on �as before� with a standard Web-Page and you will be able to log in under any user name you might already have.
There is a way you can keep BT Yahoo and the tabbed-browser, but I�ll leave that to someone else to answer for you. Personally? I do NOT like a tabbed-browser with Yahoo all over the darn place and I prefer Google for my Homepage. Good luck, and you can�t �break� anything :-)