Not sure about your compiling issues, but a PPM of Tk-PNG-2.005 already exists. It only shows up when using the PPM3 command line interface, and it's apparently not in the repository that the original PPM interface uses.

Update:
This PPM is available for Linux only. The ActiveState build I was using (631) didn't display that information. After upgrading to build 633, PPM displays the following:

Available Platforms: 1. i686-linux-thread-multi

++crazyinsomniac for pointing this out to me and prompting me to grab the latest build.

-- grummerX