Other file packers such as Winzip and Winrar will likely support the 7z format as well. On the other hand, 7-zip is free, not limited, open source and supports a lot of other formats as well, so you might actually prefer it.
The directory name is "techs" (not "techtree"), so %AppData%\megaglest\techs - you can copy and paste this to Windows (file, not Internet) Explorer - is where these files need to go. However, they might not be usable unless they have a complete techtree directory structure.
If they are just factions (i.e. there is no "resources" sub directory in at least one of these archives) you will need to copy %ProgramFilesX86%\megaglest\techs\megapack to %AppData%\megaglest\techs\, then rename the copied "megapack" directory to "old_world_dwarves" or similar, and rename the megapack.xml file in it to "old_world_dwarves.xml", too, then delete all the sub directories in %AppData%\megaglest\techs\megapack\factions\ and unpack your two archives into this directory, ending up with something similar to
%AppData%\megaglest\techs\megapack\factions\armies_of_the_old_world\ and
%AppData%\megaglest\techs\megapack\factions\dwarves\
Not exactly straight forward I guess.