I don't bother with Adobe / Acrobat Reader anymore being that Chrome and Firefox have built in capability- they also seem faster at loading than Reader.
Full installers of Firefox versions from the original 0.8 to the current Firefox 50 can be downloaded from the FTP repository:
https://ftp.mozilla.org/pub/firefox/releases/
(Select the version number, then navigate to the /win32 or /win64 directory (I don't know if the /win64 versions are compatible with XP 64-bit)
For legacy versions of Flash Player, you can always download them from Adobe's Archived Flash Player page, all the way back to version 2.0 from 1996: (for versions from 2010 to 2016, the second heading, "Flash Player archives"; for versions from 1996-2016, the last heading, "Older archives"): https://helpx.adobe.com/flash-player/kb/archived-flash-player-versions.html
Full Google Earth installers are on this page: https://support.google.com/earth/answer/168344?hl=en Google Earth 7.1.7.2606 fixed compatibility problems with Windows XP, according to this link: https://support.google.com/earth/answer/40901?hl=en
Direct full installer for 7.1 is on that page: https://dl.google.com/earth/client/GE7/release_7_1_7/googleearth-win-bundle-7.1.7.2602.exe
https://dl.google.com/earth/client/GE7/release_7_1_7/googleearth-win-bundle-7.1.7.2606.exe
Direct full installer for 6.2 is on that page: https://dl.google.com/earth/client/GE6/release_6_2_2/googleearth-win-bundle-6.2.2.6613.exe UPDATE 1/13/2019: link no longer works, use mine: http://sdfox7.com/xp/sp3/EOL/googleearth-win-bundle-6.2.2.6613.exe
The Java Archive page is here: http://www.oracle.com/technetwork/java/javase/archive-139210.html
The Opera archive page offers vintage versions back to 3.21 (2002) and is available here: http://arc.opera.com/pub/opera/win/ UPDATE 1/13/2019: link no longer works. For 16 bit Opera, go to http://www.mirrorservice.org/sites/browsers.evolt.org/browsers/opera/win16/. For 32 bit versions of Opera, go to http://www.mirrorservice.org/sites/browsers.evolt.org/browsers/opera/win/
I usually use WinRar for many files, and the current 5.40 version runs fine on XP: http://www.rarlab.com/download.htm
Direct download 32 bit is http://www.rarlab.com/rar/wrar540.exe
HOPE THIS HELPS! MERRY CHRISTMAS!