Buttons?

edit my CSS so I can add some small buttons below the header but above the top navigation bar.

You might need to edit the header.php to add the navigation items presented via buttons and add styling for new items in your theme’s style.css

the forum system I am going to use is BuddyPress.

BuddyPress is a plugin for social networking. The forum which can be installed internally via BuddyPress is bbPress forum.

Also, if you have any tips for the sub-blog, please don’t hesistate to say.

It depends on when you want to implement this project. If you could wait till May or so of this year for WordPress 3.0, you could easily set up a sub-blog and activate BuddyPress in that sub-blog instead of in the main site. In addition, you would only need one installation of WordPress, WP 3.0 that is, to manage all the sub-blogs you would like to add.
If you want to implement the project now, you could install BuddyPress if you have WP 2.9.2 and then add the navigation to the forums, groups, members, etc. in that new navigation block with buttons you want to add. Be aware that you might have to use the BuddyPress Template Pack and will have to tweak files and styles to match with your current theme’s layout.

I’m not an expert with CSS so tweaking with the files might not work out unless I have given instructions ??

Yes, making the sub-blog installed with BuddyPress would be ideal. Could I make the sub-blog’s domain community.domain.com?

Sure, you know then that since you are using only WP 2.9.2, you would need to create a subdomain named community in your hosting and that you would need to set up another WordPress install there.

In addition, if/when you do add the BuddyPress plugin, there is a forum for that plugin – https://buddypress.org/forums/ – where you can use your WP.org forum username and password to log in.

Is there a way to just install the forum but uses the BuddyPress system? Is this exactly what BBPress is?

I’d like it to look something like this:

https://blogsblog.phpmagazine.net/upload/2009/06/buddypress_101_released_-_word/buddypress.png

Is this BBPress?

Is there a way to just install the forum but uses the BuddyPress system?

You have to install WordPress because BuddyPress depends on WordPress to work. Then after you activate BuddyPress, only then can you install the internal bbPress forum seamlessly.

buddypress.png

That was the old default theme of BuddyPress activated in a WordPress Multi-User installation. The last time that theme was used as default theme was way back BuddyPress 1.1.3. The theme is not updated for current BuddyPress plugin version.

From BuddyPress 1.2 to present 1.2.3 version (which could now be installed in single WP as well), the default theme looks like this BuddyPress demo site – https://testbp.org/ with the bbPress internal install looking like this – https://testbp.org/forums/

Btw, you should read through the BP codex articles to get a better handle of what BuddyPress and internal bbPress installation are, among other pertinent info
https://codex.buddypress.org/