Steve and I wound up working on the same problem at the same time (probably for the same person…)

When working with the MSMQ adapter, keep in mind that you must reference the Microsoft.BizTalk.Adapter.MSMQ.MsmqAdapterProperties.dll to have access to MSMQ-specific properties.  (The list of properties available is in the adapter documentation.)

Why? The intellisense in the expression shape (when using the parentheses syntax on messages, ports, etc.) is looking for classes derived from Microsoft.XLANGs.BaseTypes.PropertyBase to present in the drop down list.  Some of those classes are part of your "native" BizTalk installation, some are provided by add-on adapters, and (of course) some are provided by property schemas that you develop.  A reference to the containing assembly is necessary to find them.

Other things to note relative to the MSMQ adapter:

• For dynamic send ports, the syntax can look like: SomePort(Microsoft.XLANGs.BaseTypes.Address) = @"MSMQ://FORMATNAME:DIRECT=OS:SOMEMACHINE\PRIVATE$\SOMEQ";
• In the case of dynamic send ports, the runtime will use non-transactional sends by default.  If you want transactional sends, you will need to set the transactional property: outboundMsg(MSMQ.Transactional) = true;
• Transactional messages which fail to deliver to the remote queue will be found in the local Transactional Dead Letter queue.  No error will be raised by the adapter.  This may mean that your design requires acknowledgement messages to achieve what you are looking for.