Launch LMCE with your crappy monitor attached. From a different PC on your network open a browser and type the following:http://192.168.x.xx
->Ip of your LMCE machine
This should bring up the LMCE admin page. You will see the LinuxMCE logo with the penguin sitting on the couch in the upper left hand corner. From there you can select "Media Directors" in the left hand pane. It should open up a page on the right hand side that will allow you to change the resolution. Look in the right hand corner. When you apply the changes you should see the effects immediately on your monitor.
Once you have that working, try connecting your HDTV and repeat the process.
I'm typing this from memory, so hopefully I haven't messed anything up.