You can check here: http://www.adobe.com/products/flash/about/ to see which version you should install for your Mac and OS. Note that version 10,1,102,64 is the last version available to PPC Mac users*. The latest version, 10.2.152.25 or later, is for Intel Macs only, as Adobe no longer support the PPC platform. Note that the latest Flash Player update only works on YouTube with Safari in 32 bit mode - until YouTube correct this.
* Unhelpfully, if you want the last version for PPC Macs, you need to go here: http://kb2.adobe.com/cps/142/tn_14266.html and scroll down to 'Archived Versions/Older Archives'. The first one on the list, Flash Player 10.1 is the one you download. More information here: http://kb2.adobe.com/cps/838/cpsid_83808.html
You should first uninstall any previous version of Flash Player, using the uninstaller from here (make sure you use the correct one!):
and also that you follow the instructions closely, such as closing ALL applications first before installing. You must also carry out a permission repair after installing anything from Adobe.
Download this if you haven't...
Once downloaded if it doesn't unzip automatically the double click on that file.
Look for the fp10.1.102.64_and_9.0.289.0archive folder, open it, look for the Flash Player 10.1.102.64 folder & open and look for 101r10264 folder & open it, double click on the flashplayer101r102_64_ubmac.dmg file, choose the Install Adobe Flash Player file to install... they don't make it easy!
I'm responding to your answer to Warren T. because I'm trying to solve the same problem i.e. update my Adobe Flash Player on my 1.8 ghz power pc running OSX 10.4.11. Having read your answers and that of others, I'm planning to do the following. Please confirm that I've got it right or correct me.
1) Download Flash Player 10.1.102.64 (done and waiting on my desktop).
2) Uninstall my current version of Flash Player, 126.96.36.199., following all instructions closely
3) Install 10.1.102.64.
Any tips before I go ahead? Please answer at the beginner level!
Thanks - rliptrot