You will need to ask Percy for the technical details, since this is his forum, he set it up, and he maintains it.
However, to access the past for any member, simply click on his name's link (eg, in the Author block to the left of every single message, but there are many other ways that our links are displayed). That will take you to that member's Topic Index page which lists in ascending chronological order every topic he had posted to with a link (and date-time stamp) of the last message he had posted there. For example, yours shows your brief return visit 11-17 Oct 2010, your previous last post 14-Oct-2006 9:37 PM, all the way back to your last post 30-May-2004 4:24 PM in your first topic (and coincidentally the only post in that topic). BTW, if you click on the message number link then that will take you to that topic.
And is it recorded for ever?
Depends on Percy's archiving policies, I would imagine. Your past goes back at least to 30 May 2004. Percy should be the first member (Member ID 2), so his joining date, 22-Dec-2000, should also be when he created the forum, and his first ever message was posted 24-Dec-2000 3:23 PM (BTW, times are undoubtedly PST/PDT, since that's in my personal settings).
Not to my knowledge, since Percy is not a creationist and hence should be honest. In contrast, there was one creationist, crazynutsx, who posted here briefly mainly to invite us over to his own new forum. In his case, on his own forum he would indeed resort to deleting members' messages that he could not handle and then lie about it -- another member here also joined the forum and even became an administrator, so he was able to check the forum logs and exposed that weasel's malfeasance. He ended up abandoning his forum after which Japanese hackers took it over.
Is there any compression?
Again, you would need to ask Percy for technical details.
If upon my death bed I have a life review and ...
I'm pretty sure that would be on a different server. You would need to direct your question to that server's admin.