PSXLinux-kernel-2.4.x-beta1.tar.gz seems to be the latest version. Use PSXLinux-cross-tools-i586.tar.gz to build (and no I don't know how to build it). Not sure how it works. Some more files (all dead links) can be found here
Enjoy. I came across the topic years ago and never found anything on it. So I spent some time messing with web.archive.org. Once I got a file name I googled it and found the FTP that the site was using (this is the FTP that runix.ru used to link to). Someone better figure this out.
I looked in the beta archive and found the readme:
This archive contains beta 1 release of Linux kernel for Sony Playstation - PSXLinux. PSXLinux based on uClinux 2.4.x kernel (www.uClinux.com) and contains specific support for Sony Playstation. Essential features were added: 1. virtual console over Playstation GPU improved; 2. Playstation memory card block driver improved: - some bugs fixed; - large memory card (4x,...) support added; - two memory cards into one device joining support added; 3. console over Playstation SIO added (115200, 8N1); 4. Runix hardware add-on supported: - USB host controller SL811H driver with keyboard and mouse support; - RTC support.
INSTALLATION: ------------- I. Prerequistes.
To compile PSXLinux kernel you will need: 1. Cross-compiler (egcc-1.1.2) and binutils-2.9.5 for Linux/i386 host and MIPS little endian target. Binaries may be downloaded from http://www.runix.ru or http://oss.sgi.com/mips. 2. PSXLinux kernel source tree. Download free the latest version from http://www.runix.ru.
II. PSXLinux kernel source tree installation and compilation.
1. Create directory where kernel sources will be installed an put kernel archive in it.
2. Unpack kernel archive.
gzip -cd <name>.tar.gz | tar xvf -
3. Delete stale object files and dependencies.
4. Configure kernel.
make config -- bash based configuration tool or make menuconfig -- text based color configuration tool with menus, radiolists & dialogs or make xconfig -- X windows based configuration tool
You may load one of prepared configurations from file Config (simple configuration without Runix hardware add-on support) or Config_Addon (configuration with Runix hardware add-on support).
6. Compile kernel. You will get compiled kernel 'linux' in the directory where kernel sources was installed (current directory).
7. Run compiled kernel on your game console. Visit www.runix.ru for tools an instructions.
8. Now you may mount root file system from memory card. The memory card root image, tools and instructions may be found on www.runix.ru.