Web Forms :: Assistance Required On Modifying A Validation Expression?

I have found a very useful validation expression at http://regexlib.com/DisplayPatterns.aspx?cattabindex=2&categoryId=3 However, I want to make a couple of changes but am struggling a little!!

The expression is:

^[-]?([1-9]{1}[0-9]{0,}(.[0-9]{0,2})?|0(.[0-9]{0,2})?|.[0-9]{1,2})$

As per the link, this "regular expression will match on a real / decimal / floating point / numeric string with no more than 2 digits past the decimal. The negative sign (-) is allowed. No leading zeroes or commas. It is based on a currency regular expression
by Tom Persing."

I would like to modify this as follows:

- Not match on numbers above 999
- Allow up to 5 digits past the decimal