Sean,
I have been experiencing the exact same problem, and from what I can tell after doing extensive research, it's got something to do with the way linux (and *BSD) handles the "big fast
UART" built into the novatel wireless Merlin for Ricochet PCMCIA card.
There's some more information about it
at this website, but I'm not sure what the fix is for machines running the 2.6 kernel.
I've found that if you set the low_latency flag on the serial port, that will allow you to get speeds of approx 56kps, still crappy, but better than nothing.
Not sure if linspire includes the setserial command or not, but here's what I use in the /etc/rc.local file on Ubuntu.
Code:
sudo setserial /dev/ttyS1 low_latency