Starting with Opera 7.50, there is an integrated IRC (Internet Relay Chat) client. It has all basic IRC features, including DCC file transfer (send/receive files to/from users).
IRC Commands panel - A panel with some of the most common commands you can use in Opera. Don't hesitate mailing the author if you see something missing! :-)
Like almost every other window, the chat window's look is controlled by CSS, so you can make it look almost any way you like. Here you will find some links to some pages with customized looks for chat window (they're much more beautiful than default look).
These are instructions about how to install one im.css inside your profile, instead of system-wide. Find the opera6.ini file in your profile and edit it (remember to close Opera first). Inside [User Prefs] section, add the following line:
IM Style File=/full/path/to/your/im.css
If you want, you can change all built-in Opera CSS files inside your profile. Just add these lines:
[User Prefs] IM Style File=/path/to/im.css MIME Style File=/path/to/mime.css MIME Headers Style File=/path/to/mimehead.css WML CSS File=/path/to/wml.css OPF CSS File=/path/to/opf.css CSR CSS File=/path/to/csr.css Info CSS File=/path/to/info.css Cache Style File=/path/to/cache.css Dir Style File=/path/to/dir.css Drives Style File=/path/to/drives.css History Style File=/path/to/history.css Plugins Style File=/path/to/plugins.css About Style File=/path/to/about.css