The latest version of the beta is mIRC v7.11 released on September 8th 2010 and works on Windows 2000, XP, Vista, and 7.
What is new in this beta? The full list of changes can be found in the vesions.txt file that comes with the beta. Most of the changes involve bug fixes, however there are a few notable changes, such as:
A new and improved Log Files dialog has been added that allows you to search log files and to view them in a window in mIRC.
A Clear History dialog has been added to the Tools menu that allows you to clear the history of a number of features.
File transfers now display progress bars in different colors to indicate transfer status.
DCC Send transfer speed has been improved.
A "UTF-8 encode/decode messages" option has been added to the Messages dialog to enable or disable UTF-8 encoding/decoding of server messages.
The DNS routines have been changed to only request IPv6 if you are using features that require it, which should speed up connections for some users.
And much more - there are around fifty changes in total in this release.
Source: mIRC.com