Some quick AppleScript handlers to convert between roman numerals and integers.

Roman Numerals.applescript

romanToInt("mcdxcii")
--> 1492

intToRoman(1492)
--> "MCDXCII"

on romanToInt(numeral)
	set numeral to my TextHandlers's changeCaseOfText(numeral, "uppercase")
	set n to 0
	try
		repeat while numeral is not ""
			if numeral starts with "M" then
				set n to n + 1000
				set numeral to characters 2 thru (length of numeral) of numeral as string
			else if numeral starts with "CM" then
				set n to n + 900
				set numeral to characters 3 thru (length of numeral) of numeral as string
			else if numeral starts with "D" then
				set n to n + 500
				set numeral to characters 2 thru (length of numeral) of numeral as string
			else if numeral starts with "CD" then
				set n to n + 400
				set numeral to characters 3 thru (length of numeral) of numeral as string
			else if numeral starts with "C" then
				set n to n + 100
				set numeral to characters 2 thru (length of numeral) of numeral as string
			else if numeral starts with "XC" then
				set n to n + 90
				set numeral to characters 3 thru (length of numeral) of numeral as string
			else if numeral starts with "L" then
				set n to n + 50
				set numeral to characters 2 thru (length of numeral) of numeral as string
			else if numeral starts with "XL" then
				set n to n + 40
				set numeral to characters 3 thru (length of numeral) of numeral as string
			else if numeral starts with "X" then
				set n to n + 10
				set numeral to characters 2 thru (length of numeral) of numeral as string
			else if numeral starts with "IX" then
				set n to n + 9
				set numeral to characters 3 thru (length of numeral) of numeral as string
			else if numeral starts with "V" then
				set n to n + 5
				set numeral to characters 2 thru (length of numeral) of numeral as string
			else if numeral starts with "IV" then
				set n to n + 4
				set numeral to characters 3 thru (length of numeral) of numeral as string
			else if numeral starts with "I" then
				set n to n + 1
				set numeral to characters 2 thru (length of numeral) of numeral as string
			end if
		end repeat
	end try
	return n
end romanToInt

on intToRoman(n)
	set str to {}
	repeat until n = 0
		if n ≥ 1000 then
			set the end of str to "M"
			set n to n - 1000
		else if n ≥ 900 then
			set the end of str to "CM"
			set n to n - 900
		else if n ≥ 500 then
			set the end of str to "D"
			set n to n - 500
		else if n ≥ 400 then
			set the end of str to "CD"
			set n to n - 400
		else if n ≥ 100 then
			set the end of str to "C"
			set n to n - 100
		else if n ≥ 90 then
			set the end of str to "XC"
			set n to n - 90
		else if n ≥ 50 then
			set the end of str to "L"
			set n to n - 50
		else if n ≥ 40 then
			set the end of str to "XL"
			set n to n - 40
		else if n ≥ 10 then
			set the end of str to "X"
			set n to n - 10
		else if n ≥ 9 then
			set the end of str to "IX"
			set n to n - 9
		else if n ≥ 5 then
			set the end of str to "V"
			set n to n - 5
		else if n ≥ 4 then
			set the end of str to "IV"
			set n to n - 4
		else if n ≥ 1 then
			set the end of str to "I"
			set n to n - 1
		end if
	end repeat
	set AppleScript's text item delimiters to ""
	return (str as string)
end intToRoman