This is pretty easy to do with AppleScript.
Either paste this into a new Script Editor document, or use Automator's Run AppleScript action.
-- prompt the user for the folder to process
set theFolder to (choose folder with prompt "Please select a folder")
tell application "Finder"
-- get a list of all the files in the folder
-- by default the Finder will return alphabetically-sorted list
set theFiles to every file of theFolder --whose visible is true
end tell
-- setup some variables
set subFolderName to 0
set subFolder to missing value
-- iterate through the files
repeat with i from 1 to (count theFiles)
tell application "Finder"
-- do we have an odd-numbered file?
if i mod 2 = 1 then
-- if yes, increment the subfolder name
set subFolderName to subFolderName + 1
-- and create a new folder
set subFolder to make new folder at theFolder with properties {name:subFolderName}
end if
-- move the current item into the current subfolder
move (item i of theFiles) to subFolder
end tell
end repeat
If you're only using AppleScript you might be able to simplify it a little bit by using Automator to select the folder and pass that into the script, but I generally prefer this more direct approach.
You might be able to craft this all in Automator workflows, but looping in Automator is FUBAR and I wouldn't bother when there are far easier paths.
