5300-06-03-0732
AIX fixes:
IBM Support: Fix Central
Product Group > AIX
Version > 5.3
Fix type > Fix Packs
Continue
Wait a bit while it builds the download list and then scroll / page down to "66. Service pack: 5300-06-03-0732 "
clik the tick box to the left of it, then click the box next to TL6 which should pop down below, if not then click the "Show requisite fixes" and tick TL6 as well, then click the SP title to download.
make a note of the "Installation instructions" link on the way through.
I strongly recommend going to the latest level you can, idealy the very latest.
You are going for a level that was released on 08-Aug-2007 when there was / is another six years of development in AIX 5.3, so why run such an old level if you can go to a later one. It depends on what your application supports I suppose.
HTH