Match The Output Of The PHP PACK And MD5 Functions?

I haver been struggling trying to match the output of the PHP PACK and MD5 functions.The PHP scenario I am trying to recreate in .NET is this.A 32 character hex string is passed to the PHP pack function. It returns a binary string. At this point both the .NET and PHP methods return values are the same. It works up to this point.The binary string then has a password appended to the end. This result is then sent to MD5 and it returns a hash.

When i try to do the exact same thing in .NET i never get the same result. What i have figured out is if i send a regular string to MD5 (NOT a binary string created from the pack functions) I do get the same result every time both in .NET and PHP.However, if i send the binary string to MD5 in PHP and .NET I get different results.