Certain Wi-Fi network not available on Motorola Milestone with Cyanogenmod
There are two possibilities:


If your WLAN is running in 2.4GHz mode you should chekc the used channel. Not all channels are allowed in all countries - especiall in the US the channels higher than 13 are AFAIK forbidden. Therefore some devices do not even scan the frequencies that belong to those channels. What frequencies/channels are used is specified by the driver/firmware - therefore using CM7 my be the problem. Try to cache your WLAN access point config to use a lower WLAN chennel.
Your WLAN is running in 5GHz mode only. Only devices with 5GHz capable WLAN hardware can use a WLAn that is operating in 5GHz only mode. Unfortunately the number of smartphones that are 5GHz capable is very short. Therefore you should check your WLAN access point config if it is in 5GHz only mode and if so change it to dual frequency mode 2.4GHz + 5Ghz running at the same time.