Ok i figured this out. Here is the code for anyone else that wants to put the last posts on their home page etc. I put mine in a scrolly box. You will need to change yourserver/folder and tabid to suit.

I have some Private forums. I didn't want posts appearing from private forums so I excluded these in my SQL. I also check that a forum is active and that a post has been approved. There's probably a much easier way to do this but I'm a dotnetnuke and SQL beginner so be kind

SELECT  Top 10  '<a href="http://yourserver/dotnetnuke/forums/tabid/163/forumid/' + cast(Forum_Forums.ForumID as varchar(3)) + '/threadid/' + cast(Forum_Threads.ThreadID as varchar(3))  + '/scope/posts/Default.aspx">' + Forum_Posts.subject + '</a>' From Forum_Posts inner join forum_threads on Forum_Posts.ThreadID = Forum_Threads.ThreadID inner join Forum_Forums on Forum_Threads.ForumID = Forum_Forums.ForumId inner join Forum_Groups on Forum_Forums.GroupID = Forum_Groups.GroupID where Forum_Groups.Name <> 'Private' and Forum_Forums.isactive = '1' and Forum_Posts.isapproved = '1'
order by cast(Forum_Posts.PostID as varchar(3)) desc

Cheers,

Simon