Both wireless stations and Ethernet stations will participate in the same (private) subnet. They will be able to communicate with each other to share files, and will be able to communicate through the router to share Internet access. The wireless router will probably NAT all Internet-bound traffic and act as a DHCP server for all stations.
Details and capabilities depend on which wireless router you are using, but this configuration is fairly common and probably supported by your DSL/wireless router.
This was first published in August 2004