The title says it all. The current version 1.8.1.1087 of PixInsight is the last one that will be released for 32-bit Windows platforms. It will continue being available for download for a long time, but it is unsupported and won't be updated anymore, unless some critical bugs are discovered. Note that this was
announced officially in June of 2012.
From now on, only 64-bit versions of PixInsight will be released for FreeBSD, Linux, Mac OS X, and Windows.