I would like to add details such as my website address to my exif data. I cannot find reference to altering the exif data in the manual. can anyone help?

Best way is to create an action in photoshop which does it for you.  Just go to "file information" in the "file" menu and you will find all sorts of things in there which attach themselves to the exif which you can modify.  I have said action as part of my resize for web - it also puts a copyright symbol on it, so that if the file is opened up in photoshop or other image editing programs which suppport the feature, it will remind whoever is opening the image that it is indeed copyrighted as it will have the © next to the title in the title bar.

You can do it in Photoshop as Rich mentioned, and if you have Adobe Bridge, that will give you more automated functions... Also in Photoshop, if you open File Info, on the upper right you'll see a triangle; you can save templates for any kind of additional information that you wish to add to your 'XMP metadata'.

Btw, the advantage of using Adobe Bridge (if you have it) is that you don't have to reopen your files and resave them, thus preventing that you lose quality by 're-JPEGging'... In Bridge, you can select hundreds, thousands of files and add the metadata information you want all at once.