Issue adding a custom DLL file to BIDS

I came across this download mail task on Codeplex & would like to implement it.  The download should be basic as it includes 3 files:

• DownloadMailTask.dll
• ICSharpCode.SharpZipLib.dll
• INSTALL.txt

The instructions are equally basic.  Copy files the designated folder & copy them again to the C:\windows\assembly.  Then follow these steps.

1. Open BIDS
2. Right Click Toolbox
3. Click Choose items
4. Click 'SSIS Control Flow Items'
5. Check off 'Download Mail Task'
6. Click OK

It all seems painfully simple, except when I get to step 4, I don't see 'Download Mail Task'.  So I retraced my steps
Codeplex suggests that the file should be inC:\Program Files\Microsoft SQL Server\90\DTS\Tasks.  But the Tasks folders for me are

• C:\Program Files\Microsoft SQL Server\100\DTS\Tasks
• C:\Program Files (x86)\Microsoft SQL Server\100\DTS\Tasks

I went so far as to create the folder structure that it expects, but it did not work.  I also opened/closed BIDS & rebooted the computer between.  Does anyone know what I might have missed?

EDIT: I originally tried this on a Windows XP 64bit box with SQL Server 2008 & BIDS 2008. 
I later tried it on a Windows XP 32bit box with SQL Server 2005 & BIDS 2005 (due to something I read in this thread) but the results are the same.