I just opened an account, set up email/username/password etc then clicked the "upload" button on the main screen. I was then able to select pictures from my computer to upload onto Photobucket.
Once the pictures are on Photobucket ~ you then go to "links to share this photo" which is on the right hand side of the photos ~ click direct link to copy it.
Then when on the 350Z forum you just click on the add "image" icon in the reply box and paste the link in there. That's how I did it.