To achieve this in the SQL version you should go...

forum_topics.asp

where it says:
 <tr>
  <td align="left" class="bold"><img src="<% = strImagePath %>open_folder_icon.gif" border="0" align="absmiddle">&nbsp;<a href="default.asp" target="_self" class="boldLink"><% = strMainForumName %></a><%
 
Response.Write(strNavSpacer)

should say:
 <tr>
  <td align="left" class="bold"><img src="<% = strImagePath %>open_folder_icon.gif" border="0" align="absmiddle">&nbsp;<a href="default.asp" target="_self" class="boldLink"><% = strMainForumName %></a>
 </tr>
 <tr>
  <td align="left" class="bold">&nbsp;&nbsp;&nbsp;<img src="<% = strImagePath %>open_folder_icon.gif" border="0" align="absmiddle" class="boldLink">&nbsp;<a href="default.asp?C=<% =rsForum("Cat_ID") %>" target="_self" class="boldLink"><% = rsForum("Cat_Name") %></a>
 </tr>
 <tr>
  <td align="left" class="bold">&nbsp;&nbsp;&nbsp;&nbsp;& ; ; ;nbsp;&nbsp;<img src="<% = strImagePath %>open_folder_icon.gif" border="0" align="absmiddle" class="boldLink">&nbsp;
  <%

'Response.Write(strNavSpacer)

------------------------------

forum_posts.asp

where it says:
 <tr>
  <td align="left" width="95%" class="bold"><img src="<% = strImagePath %>open_folder_icon.gif" border="0" align="absmiddle">&nbsp;<a href="default.asp" target="_self" class="boldLink"><% = strMainForumName %></a><%
 
Response.Write(strNavSpacer)

should say:
 <tr>
  <td align="left" width="95%" class="bold"><img src="<% = strImagePath %>open_folder_icon.gif" border="0" align="absmiddle">&nbsp;<a href="default.asp" target="_self" class="boldLink"><% = strMainForumName %></a>
 </tr>
 <tr>
  <td align="left" class="bold">&nbsp;&nbsp;&nbsp;<img src="<% = strImagePath %>open_folder_icon.gif" border="0" align="absmiddle" class="boldLink">&nbsp;<a href="default.asp?C=<% =rsPost("Cat_ID") %>" target="_self" class="boldLink"><% = rsPost("Cat_Name") %></a>
 </tr>
 <tr>
  <td align="left" class="bold">&nbsp;&nbsp;&nbsp;&nbsp;& ; ; ;nbsp;&nbsp;<img src="<% = strImagePath %>open_folder_icon.gif" border="0" align="absmiddle" class="boldLink">&nbsp;
<% 
'Response.Write(strNavSpacer)

----------------------------

Stored Procedures changes:

wwfSpThreadDetails should be:
CREATE PROCEDURE [dbo].[wwfSpThreadDetails] (@lngTopicID int) AS
SELECT  tblTopic.*, tblThread.*, tblAuthor.Username, tblAuthor.Homepage,
tblAuthor.Location, tblAuthor.No_of_posts, tblAuthor.Join_date,
tblAuthor.Signature, tblAuthor.Active, tblAuthor.Avatar, tblAuthor.Avatar_title,
tblGroup.Name, tblGroup.Stars, tblGroup.Custom_stars,
tblCategory.Cat_ID, tblCategory.Cat_Name
FROM tblTopic, tblThread, tblAuthor, tblGroup, tblForum, tblCategory
WHERE tblTopic.Topic_ID = tblThread.Topic_ID  AND tblAuthor.Author_ID = tblThread.Author_ID
  AND tblAuthor.Group_ID = tblGroup.Group_ID AND tblTopic.Topic_ID = @lngTopicID
  AND tblForum.Forum_ID = tblTopic.Forum_ID
  AND tblCategory.Cat_ID = tblForum.Cat_ID
ORDER BY tblThread.Message_date ASC;
GO

------

wwfSpForumsAllWhereForumIs should be:
CREATE PROCEDURE [dbo].[wwfSpForumsAllWhereForumIs] ( @intForumID int )  AS SELECT tblForum.*, tblCategory.Cat_Name, tblCategory.Cat_Id FROM tblForum INNER JOIN tblCategory ON tblForum.Cat_ID = tblCategory.Cat_ID WHERE Forum_ID = @intForumID;
GO

I would add this in the Mod's forums.... but I don't have access to post in there. May I add the code in here anyway?

I think it should be useful to place the name of the category we're in. Have a look at the picture:

As you might think there could be many forum's "bugs" within the Forums. Especially if the forums are for different application. The same happens with "Suggestion" or any other forum.

One way to solve this could be to include the name of the category in the name. In the image's example should be "DokuViz.Bugs" (or could just be DV.Bugs).

By the way, I like the treeview's idea (image above) better, so that's how I modified the forums's code to show this information.