BTW, MSMQ adapter for BizTalk 2004, that I referred to before, is now available for download at http://www.microsoft.com/downloads/details.aspx?FamilyID=cba87d07-7f50-4d7b-a888-388d123f736e&DisplayLang=en

That's the same adapter, I previously referred to as "MSMQ/C". This is a pretty good alternative to MSMQT adapter shipped in-box. Here are just few thinmgs that differs between MSMQ/T and MSMQ Adapters:

If you want to... MSMQ/T Adapter (in-box) MSMQ Adapter (new)
Run other applications that use MSMQ API (or simply use MSMQ API at all.) Only if you install Windows message queuing (MSMQ) side by side with MSMQT. Automatically granted, in fact, MSMQ Adapter itself is using Windows MSMQ API.
     
Deliver messages reliably and in order to the BizTalk application (orchestration). Example, when you may need it: financial applications, where customer orders must be executed in the same order as they are received. That's what MSMQ/T is for. In fact, that's the only way to reliably do that in BizTalk 2004, short of implementing your own application level protocol. No, you cannot use MSMQ Adapter for that in BizTalk 2004.
     
Reliably push as many messages onto the BizTalk machine as possible (but not yet into BizTalk per se). Example, when you need it: sending messages from an unreliable machine that may go down for a significant period of time. Tough, MSMQ/T submits messages directly into BizTalk, hence it gets messages from the network only as fast as BizTalk can consume them. Perfect. Messages are accumulated on the local disk of BizTalk machine in MSMQ queue with usual MSMQ throughput (huge one). Then BizTalk picks it up from the local queue at its own pace.
     
Pass huge messages (see BizTalk docs for the exact numbers) Good. MSMQ/T has everything streamed, so for large messages there is no single moment in time when the whole message must be in memory. As a result, MSMQ/T messages by design should be only limited by the size of your database. Keep in mind, however, that it is only supported to a certain limit stated in the documentation. Also, if your database has 2Gb of a disk space, it may be not quite a bright idea to fill it with 1Gb blobs. You still can pass pretty large messages, however, MQRTLARGE.DLL that is utilized by MSMQ Adapter, accumulates the whole message in memory, effectively limiting the size of a message you can pass through.