These packages are stored in the msdb database in the dbo.sysSSISpackages table.
The following msdn link shows all the columns and their descriptions:
http://msdn.microsoft.com/en-us/library/ms181582.aspx
We needed to get to the raw XML for one of the packages as it didn't appear to be in our source control. The above link told us that the code is stored in the column PackageData. Unfortunately, it appeared to be encoded.
After a bit of searching I found the following code to convert the code back to the XML.
--------------------------------------------------------
-- Get XML from encoded column
--------------------------------------------------------
SELECT
Name
, CONVERT( xml, CONVERT(varbinary(max),PackageData) )
AS XMLSource
FROM msdb.dbo.sysssispackages
