The newest mIRC version (6.34) has been released on (August 8^th 2008)

Take your time when upgrading from a previous version. You will notice the mIRC installer changed and improved quite a bit. If you want to keep your old settings, tell the installer to not install the 'Settings File' (mirc.ini) and 'Scripts' (aliases.ini and popups.ini). And whatever you do, the installer makes a backup by default :-)

mIRC can be downloaded freely and evaluated for 30 days. If you find that you like mIRC, and wish to continue using it after the evaluation period, you are required to register it. Your registration will license you to use current and future versions of mIRC.

mIRC 5.91 was the last version that came in both a 32 and a 16 bit issue. Over the past years less and less people were using the 16 bit issue. All current Windows versions work with the 32 bit issue. There are no configurations left that demand for the 16 bit issue on Windows 95 and above and old 16 bit winsocks do not exist anymore. These considerations made us stop development of the 16 bit mIRC issue. The most recent 16 bit mIRC 5.91 cabinet is named mirc591s.exe (16bit, 1070080).
You can still download this old version from mIRC.org.