PHP 5.1.6 is already out
[24-Aug-2006] The PHP development team would like to announce the immediate availability of PHP 5.1.6. This release contains a fix for memory_limit restriction on 64 bit systems that was not included in PHP 5.1.5.
Change log:
Fixed memory_limit on 64bit systems. (Stefan E.)
Fixed bug #38488(Access to "php://stdin" and family crashes PHP on win32). (Dmitry)
If you are lucky enough to run a Debian 3.1 based server, you might want to add the DotDeb.org apt repository in /etc/apt/source.list:
deb
http://packages.dotdeb.org stable all
deb-src
http://packages.dotdeb.org stable all
It took me only 5 seconds to upgrade the PHP version on my server over DotDeb