I've got a collection of functions like that that strip out certain characters, html encode data, etc, all based on Jeff Moden's Tally Table concept.

Try this out for size: it's really fast:

[font="Courier New"]

    --===== Create and populate the Tally table on the fly

SELECT TOP 11000 --equates to more than 30 years of dates

            IDENTITY(INT,1,1) AS N

            INTO dbo.Tally

    FROM MASTER.dbo.SysColumns sc1,

            MASTER.dbo.SysColumns sc2

    --===== Add a Primary Key to maximize performance

ALTER TABLE dbo.Tally

            ADD CONSTRAINT PK_Tally_N

            PRIMARY KEY CLUSTERED (N) WITH FILLFACTOR = 100

GO

CREATE FUNCTION StripNonNumeric(@OriginalText VARCHAR(8000))

RETURNS VARCHAR(8000)

    BEGIN

    DECLARE @CleanedText VARCHAR(8000)

    SELECT @CleanedText = ISNULL(@CleanedText,'') +

        CASE

            --ascii numbers are 48(for '0') thru 57 (for '9')

                    WHEN ASCII(SUBSTRING(@OriginalText,Tally.N,1)) BETWEEN 48

                AND  57  THEN SUBSTRING(@OriginalText,Tally.N,1)

        ELSE '' END

        FROM dbo.Tally          

        WHERE Tally.N <= LEN(@OriginalText)

    RETURN @CleanedText

    END

GO

SELECT dbo.StripNonNumeric('Alex is 25 years old on 01/14/2008')

    --results 2501142008[/font]