The "tb" folder is the thumbnails folder. The folder is automatically created by the Homepage application, and thumbnails are generated for each picture in your Pictures folder. You may not be able to delete those if the WebObjects application behind Homepage retains ownership of the files. I don't know if or how the folder is updated if you delete the original pictures.
As for not being able to access your pages, are you referring to access via the Homepage application or for just regular web browsing use? I've noticed that there must be a rather "robust" caching on Apple's servers. After I had updated my pages and sent out a note to friends to check it out, at least one person who had NEVER been to my site before got the PREVIOUS version of the pages. Strange...