I'm happy to report that despite a bug in either g++ or gcc (whatever boost is written in) I was able to compile QT, Boost and Speex on my host's server. Having done all that I notice that the server's build itself is dependant only upon QT?
I can connect to the server just fine with the prebuilt .exe client on windows but I didn't try logging in with the superuser (maybe this was my mistake). Instead, I logged in from my laptop and desktop as two unauthorised users with arbitary names and expected to be able to communicate between the two. Unfortunately I was unable to hear any sounds from the desktop on the laptop and vica-versa. Is this because I failed to do any configuration first as the super user (I'm back at work now so cannot check) or is there some other reason you can think of? Also, I connected to the server at mumble.saarwave.de and was able to communicate between the two clients without problems, so it's a server thing.
Many thanks for any help you can offer,
My host has denied UDP packets are being blocked which leaves me suspecting something in my own configuration. When next I get some time I'll analyse my own network logs more thorougly.
It sounds like your server is blocking UDP packets. Mumble/murmur use TCP for control data (guaranteed in-order delivery) and UDP for the actual voice (reduced overhead and latency). Hence, if you specify port 1234, it will open both port 1234/tcp and 1234/udp.
For testing, you can try to enable TCP mode on both clients, but be aware that such a setup will have much worse performance (and sound more choppy) so it's not recommended for a "production" system.