It looks likes you have two options:
There is an ALT Code you can try to type. To try it:
- Hold down the ALT key on your keyboard
- Using the number pad (it must be the number pad), type 2, then 1 (21). Make sure Num Lock is on.
- Release ALT and it should type a §
On Mac, it looks like if you hold ALT and type 6, it will type the § sign (ALT and 5 for extended U.S. keyboards).
The other way is to use plugins that replace the § with something else. Looking around, it seems CommandBook for Bukkit may work.
Sources: Minecraft Wiki, Talk:Formatting codes
