Although a very old thread, interesting to read the answers given.
Focusingscreen.com does give very detailed instructions, @pishta gave the correct link:
PENTAX K100D / K200D / K2000D / K-m / K-x / K-r Focusing Screen Installation Instruction
The screen used in the K-x is the same one as used in the old *ist-DL, K100D, K110D, K200D and K-m (K-2000)
All those suffer a bit because the use the penta-mirror viewfinder 0,85x 96% (95% in istDL which was a degradation of the *ist-D/DS/2 with pentaprism 0,95x 95%)
Also the screen in the *istD/DS/DS2 series was superior, but wouldn't fit into those, tiny bit smaller.
The orig. *ist-DL/2, K100D, K110D, K200D, K-m and K-x screen was called L-90!
It was similar to the LL 80 of the K10D and K20D and had the same difficulties for manual lenses but no alternative, the LL 80 of the K10D/K20D could be replaced with the L60/ML60 of the *istD/DS/DS2 because those had the same 0,95x 95% pentaprism viewfinder.
So any screen by Katzeye or Focusingscreen.com was really superior.
Cleaning the screen:
if a Giotto won't do it, try holding the screen as described here into the stream of a vacuum-cleaner:
Help ! Cleaning a focusing screen - PentaxForums.com
I also described there how you wet-clean a screen without any danger.
Have done it many times, never once a spec of dust or other residue.