The new version of mIRC will only run under Windows 2000, XP, Vista, and 7.
It is no longer possible to run the new version of mIRC under older versions of Windows, such as Windows 95/98, since they cannot run Unicode applications natively, and any Unicode support that they do have is very limited. It was only with Windows 2000 and onwards that Unicode became a viable and practical option for applications.
At some point, I have to decide when to drop support for an older version of Windows. I usually maintain support for as long as I can - for example, Windows 3.1 was supported for many years, long after most developers dropped support for it, and even though very few people used it.
In the same way, I held back improvements in mIRC to support Windows 95/98, even though very few people were using those versions of Windows. At this point, Windows 95/98 register barely, if at all, in any global usage statistics. So it does seem a reasonable point to drop support for them and to allow mIRC development to move forward.
I have just added a section to the beta page
that indicates which versions of Windows are supported.