This is a great extention to have for mssql. There is more information about what the function does on the levenshtein wiki page in short it will give you a number of changes (add / delete / change) to get from the first string to the second string.

For example: "Hello World" and "Hello Worlds" has a distance of 1. This can be great if you are trying to do searches where you want to pick up on typo's or spelling mistakes.

The c# code for the extenstion is

[Microsoft.SqlServer.Server.SqlFunction(IsDeterministic = true, IsPrecise = false)]
    public static SqlInt32 Levenshtein(SqlString S1, SqlString S2)
    {
        if (S1.IsNull || S2.IsNull)
            throw (new ArgumentNullException());

        int n = S1.Value.Length;
        int m = S2.Value.Length;

        int[,] d = new int[n + 1, m + 1];
        int cost = 0;

        if (n == 0)
            return m;
        if (m == 0)
            return n;

        for (int i = 0; i <= n; i++)
            d[i, 0] = i;

        for (int j = 0; j <= m; j++)
            d[0, j] = j;

        for (int i = 1; i <= n; i++)
        {
            for (int j = 1; j <= m; j++)
            {
                if (S1.Value[i-1] == S2.Value[j-1])
                    cost = 0;
                else
                    cost = 1;

                d[i, j] = System.Math.Min(System.Math.Min(d[i - 1, j] + 1, d[i, j - 1] + 1), d[i - 1, j - 1] + cost);
            }
        }

        return d[n, m];
    }

Once compiled you can create a function for mssql woth the following code.

CREATE Function Levenshtein(@S1 nvarchar(512), @S2 nvarchar(512))
	RETURNS int as EXTERNAL NAME SqlExtensions.UserDefinedFunctions.Levenshtein
GO

You can read more about enabling clr support in mssql here

Adding an MD5SUM function to MS SQL.

public partial class UserDefinedFunctions
{
    [Microsoft.SqlServer.Server.SqlFunction(IsDeterministic = true, IsPrecise = false)]
    public static SqlString MD5Sum(SqlString S1)
    {
        MD5 md5 = System.Security.Cryptography.MD5.Create();
        byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(S1.Value);
        byte[] hash = md5.ComputeHash(inputBytes);

        // step 2, convert byte array to hex string
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < hash.Length; i++)
            sb.Append(hash[i].ToString("X2"));

        return new SqlString(sb.ToString());
    }
}

You will also need to following SQL To install the function

CREATE Function MD5Sum(@S1 nvarchar(512))
	RETURNS nvarchar(64) AS EXTERNAL NAME SqlExtensions.UserDefinedFunctions.MD5Sum
GO

You should be able to call the function in normal sql code like SELECT dbo.MD5SUM('test value')

More about enabling .NET CLR In SQL Server