Hi Ana!
WinNonlin 5.3 (without PHX) was released in December 2009 and is availalbe for download in our support site. The documentation has not changed but it was uploaded to this website in March. We apologize for the confusion.
I see. Would have been nice to be notified about the new release. I found the information by chance here. Going to 'Home > Library > Support > Product Downloads' ended in electronic nirvana - so I assumed WNL5.3 wasn't released yet.
Please note that the released version of Phoenix WinNonlin 6.1is supported on Windows 7 and Vista 32-bit only.
What? To quote *Phoenix 1.1 Getting Started Guide' > Installation > Supported operating systems: Windows 2000 SP4, Windows XP Pro SP3, Windows 2003 Citrix Server, Windows Vista 32 bit.