Let Cydia do it's updates (should be one of them little red blobs on it to tell you it needs an update) as that will update any revisions to any of the software you have installed via Cydia - basically the same way if an iTunes App Store app you have installed needs an update, it will tell you...

SwirlyMMS works fine on 2.1, and as far as I know, it sends the MMS just like any other phone - you can input a message title/subject, type text into it (or not if you don't want to) and attach a picture, media file, whatever. I've only used it to send pics, and only sent three, but they were recieved okay, and I've recieved 2 that I've been sent no problem.... The only thing with it not being a native part of the OS means that when you take a picture with the camera, for example, and you can click the button to give you options to send as email etc, there isn't one to send as MMS. You have to tap Swirly and then look the pic up using thier interface.....