It's bound to be complicated, as networks were never designed for the home. You are moving into a commercial area, and whether you are connecting just two PC's together or a hundred is irrelevant.
For starters, check your ME workstation is in the same Workgroup as the XP machines and that it has a unique name.
How have you tried to set it up - via a Wizard from XP? or some other means. Is it set-up to obtain an address from your router? It should be. If you have a static address nominated on the machine, you have to make sure that it's in the same range of addresses that the router is currently using.
Finally (for now) make sure you are using a patch (straight through) cable. Although some routers will automatically recognise and compensate for crossover cables, they are in the minority. You could also temporarily try the cable connected to the XP machine and see if your wireless XP machine sees the ME computer. If it does, it could simply be a cable problem.