Someone asked this on the Samsung forum and their reply appears to be:
There is no setting on the phone to delete words from the T9 dictionary. The only way to do this would be for an engineer to flash the software on the phone, which will delete everything from the phone. . You can arrange this by going to your local Samsung authorised service centre. To find the closest one to you go to the support page of our website (http://www.samsamsung.co.uk/) and select Service locations. You will need to back up anything on the phone you do not wish to lose before going. I suggest that you also phone the service centre to make sure the engineer will be there and take along your proof of purchase. Alternatively you can arrange to post the phone to us by calling on 08456 726 7864 or by going to the Support page of our website and selecting Online repair service.
Extremely irritating and I shan't be buying another Samsung that's for sure!
ste
February 2010