Adding Extension to end of file names

Hi I am having trouble here, I know this can be done I’m just going about it the wrong way.
I need to move files from a mac to a pc, the pc of coarse needs file extensions to know what the files are, I have several documents and spreadsheets that need to have the .doc or .xls extension at the end of the file name. in other words if you have a file named this is my file that is a spreadsheet it would need to be this is my file.xls does this make scence. also if possible it needs to limit the characters to 25 so win 95 can use it. Thanks

Apple supplied an Applescript for this, I hope it works in OS versions earlier than OS X…

(*
Add Prefix-Suffix to File Names

This script is designed to add a prefix or suffix to files in the front window of the desktop.
If no folder windows are open, the script will effect items on the desktop.

Copyright © 2001 Apple Computer, Inc.

You may incorporate this Apple sample code into your program(s) without
restriction.  This Apple sample code has been provided "AS IS" and the
responsibility for its operation is yours.  You are not permitted to
redistribute this Apple sample code as "Apple sample code" after having
made changes.  If you're going to redistribute the code, we require
that you make it clear that the code was descended from Apple sample
code, but that you've made changes.
*)

-- The following line is disabled due to a Menu Manager bug
--set the source_folder to (choose folder with prompt "Pick the folder containing the files to rename:")

try
	tell application "Finder" to set the source_folder to (folder of the front window) as alias
on error -- no open folder windows
	set the source_folder to path to desktop folder as alias
end try

set the prefix_or_suffix to ""
repeat
	display dialog "Enter the prefix or suffix to use:" default answer the prefix_or_suffix buttons {"Cancel", "Prefix", "Suffix"}
	copy the result as list to {the prefix_or_suffix, the button_pressed}
	if the prefix_or_suffix is not "" then exit repeat
end repeat
set the item_list to list folder source_folder without invisibles
set source_folder to source_folder as string
repeat with i from 1 to number of items in the item_list
	set this_item to item i of the item_list
	set this_item to (source_folder & this_item) as alias
	set this_info to info for this_item
	set the current_name to the name of this_info
	if folder of this_info is false and ¬
		alias of this_info is false then
		if the button_pressed is "Prefix" then
			set the new_file_name to the (the prefix_or_suffix & the current_name) as string
		else
			set the new_file_name to the (the current_name & the prefix_or_suffix) as string
		end if
		my set_item_name(this_item, the new_file_name)
	end if
end repeat
beep 2

on set_item_name(this_item, new_item_name)
	tell application "Finder"
		--activate
		set the parent_container_path to (the container of this_item) as text
		if not (exists item (the parent_container_path & new_item_name)) then
			try
				set the name of this_item to new_item_name
			on error the error_message number the error_number
				if the error_number is -59 then
					set the error_message to "This name contains improper characters, such as a colon (:)."
				else --the suggested name is too long
					set the error_message to error_message -- "The name is more than 31 characters long."
				end if
				--beep
				tell me to display dialog the error_message default answer new_item_name buttons {"Cancel", "Skip", "OK"} default button 3
				copy the result as list to {new_item_name, button_pressed}
				if the button_pressed is "Skip" then return 0
				my set_item_name(this_item, new_item_name)
			end try
		else --the name already exists
			--beep
			tell me to display dialog "This name is already taken, please rename." default answer new_item_name buttons {"Cancel", "Skip", "OK"} default button 3
			copy the result as list to {new_item_name, button_pressed}
			if the button_pressed is "Skip" then return 0
			my set_item_name(this_item, new_item_name)
		end if
	end tell
end set_item_name