I was looking through satoshi's profile and saw that he was the 3rd user registered on the forum. The 1st user on the forum was a user called "admin" I tried looking through this user's post and it says that there were no matches found. The user was registered 2 days before satoshi was registered. This user had the rank called "Newbie" (which I currently have.) This user had been active at least 7 times and he was active for 5 days until he went offline. Is the user "admin" one of satoshi's accounts?
I think that user admin is created automatically when this forum software is installed on a server. Probably the creator of this forum never used that account to post anything. Most likely he immediately created his own account.
What will really blow your mind is that satoshi himself never posted on bitcointalk at all. It was hosted on a different domain back then and it wasn't until satoshi's "disappearance" that bitcointalk came to be. As for your question, satoshi wasn't the admin of the old forum and joined after it was up and running. If you use the search feature you'll get a lot more detailed knowledge about exactly who started the forum and the timing involved. In the meta section this has been discussed quite a bit over the years so you should be able to find a few detailed topics fairly easily if you search there.
Honestly, I'm here for almost five years and even I didn't know that. Now I feel a little embarrassed that I didn't know that. I always thought that Bitcointalk was created around the same time Bitcoin was created so that creators had a place to discuss.