I was a little disapointed to see that in the WP-admin post page there are HTML creating buttons in every browser except Safari. So I did a little digging and found that aparrenly (according to the PHP source) Safari does not support the javascript necessary to preform some of the functions. I dd not accept this as being gospel and went digging through the source a little more and realized that I was over my head trying to fix the javascript. Instead I just edited the browser snifffing code and enabled the HTML functions for Safari. The only real issue seems to be that the cursor does not get inserted back into the correct place. A minor annoyance IMHO. As long as you add your HTML tags as you type. If you add HTML after you type your post this is a little more than annoying, actually it make the feature almost useless and I can understand why Matt chose to use some browser sniffing to hide it from Safari. (Hello, Dave Hyatt? r u listening?)
With that caveat I give you the edited (ok, only needed to remove one character) PHP file for the admin-functions of WordPress. This should be placed in the wp-admin directory. And as always make a backup of the original file (eg: admin-functions.org.php).
Note: This applies to the current and previous versions of WordPress ( >= 1.5.1).