Well it is absolutely a good start, first on the home page I'd set the animated logo to loop just once or maybe twice, otherwise it starts to get distracting and once there's more content that'd be a problem.
On the forums, I think if you tinkered with changing the header bgs to gradients it would really be a great and simple improvement.
Also, Signatures is spelled wrong as forums, not a major prob, but thought you'd like to know
To move things around in the header, you'll have to go to inc_header.asp and try and read through the code to get a feel for what it does. to move the links, look for where it says call sForumNavigation and if you paste that somewhere else, it'll have the links come up in that different location. So maybe after the main table opens you could put
Response.Write " <tr>" & vbNewLine & _
" <td align=""center"">" & vbNewLine
call sForumNavigation
Response.Write " </td>" & vbNewLine & _
" </tr>" & vbNewLine
This would center the links above your forum, in adition you could do it below the first row where it has Forum, Topics, etc.
Just play around with it and try different things out just make sure to backup your files before you start editing them because it's very easy to mess things up and forget what change you made.