OK, this one here works with the Page Setup dialog window of Microsoft Word. Try it with SnagIt (replace the process name in line 2):
tell application "System Events"
tell application process "Microsoft Word"
tell window 1
tell radio group 1
tell (first radio button whose description is "Landscape")
if value of attribute "AXValue" is not 1 then perform action "AXPress"
end tell
end tell
end tell
end tell
end tell
Note: I added the value check for the button also to the Scapple Print dialog script above. Please use the new version!
(Without value check the script would deselect an already selected Landscape button.)