At the risk of getting into trouble with my fellow members for being too nice, you did go about it in the wrong way.
Many of the members like to know who has joined the forum recently; this in usually done by putting a little bit about yourself in the section coincidentally called "Introduce Yourself" before you dive into the rest of the forum.
Next, your first post did come across as a bit of a "I've got a Td5 which I can't do anything with, what will you give me for it?" which frankly does sound like a bit of spam on the boards.
Hence the abuse.
So far as selling on the forum is concerned, yes, we do have a "For Sale" section open to all members once they have made 50 contributions to the boards. This rule is to stop people coming on here just to sell their stuff; we don't know you from Adam, so how do we know that the stuff is cosher?
So what you need to do now is to go to the Introduce yourself bit, then re-word your post a bit and just get used to the abuse on here, it's just banter.
So far as your Disco is concerned, mine is a Landmark too, I'd be tempted to get it all fixed, 100k miles is just out of the running in period. Treated properly, you've got quite a nice bit of Land Rover, even if you have to pay someody to do the work for you.