CAML Query against content type

Question

Hi
I am trying to query a Document library by content type using CAML:
SPQuery qry = new SPQuery();
string query = <Where><BeginsWith><FieldRef Name='ContentTypeId'/><Value Type='Text'>0x0101003de59dc6676b4ab49e4eb231a59ac906</Value></BeginsWith></Where>;
qry.Query = query;
SPListItemCollection items = docLib.GetItems(qry);
int itemCount = items.Count(); //this is 0
When I run this, no items are returned.  However, when I go into the default view of the document library and filter against the content type, I can see documents are associated to that content type.  Was wondering why I can see the documents
in the filtered default view, but the CAML query does not return any items. 
Any advice or direction to some online resource would be greatly appreciated.
Thank you in advance
Rachael

Answer 1

I tested on a document library with document content type, the following two works:
<Where><BeginsWith><FieldRef Name='ContentTypeId'/><Value Type='Text'>0x0101007764851CB5A6344EB5C9E35447D01F39</Value>
<Where><BeginsWith><FieldRef Name='ContentTypeId'/><Value Type='Text'>0x0101</Value>
0x0101007764851CB5A6344EB5C9E35447D01F39 is the content type id of the list content type and 0x0101 is the content type id of the site content type.
but what follows does not work:
<Where><BeginsWith><FieldRef Name='ContentTypeId'/><Value Type='Text'>0x01010</Value>
By the way, i sugguest using the value type ContentTypeId instead of Text as the CAML generated by LINQ described in: 
http://msdn.microsoft.com/en-us/library/ff798478.aspx