>> Is it possible to install other guests other than Squeezebox on domU? If yes , how?
SqueezeOS is currently the only guest (kernel + rootfs) we support on domU. We are currently working on porting other Linux distributions/stacks on domU and will post updates on SourceForge when we will have a working environment.
We are also planning to port other OS to run on domU but this will come in a second step.
>> Do xm commands work in dom0 or domU?
xm commands and other userspace utilities are not supported in EmbeddedXen. Since we do not create domains dynamically and do not already support migration and dynamic control over domains (suspend/save/resume/restore) we don't need such tools. We will perhaps sometimes support some of these tools or a subset of their functionality (for guest migration for example) but we have no precise roadmap for these features.