First - I don't have a DCS2120, and as a matter of fact I don't even have a wireless camera - as far as I'm concerned wireless networks should be used for mobility, so if the camera isn't mobile, then wire it.
You, of course, are entitiled to your opinion, so you understand, up front, that YOU are going to have to go dig out the manual for you camera and do some reading.
Setting up a wireless camera should be no more difficult than setting up any other wireless device - which essentially requires two areas to be addressed - the SSID and the security. There are other aspects, such as ip addressing, but, if you have the camera working wired, I assume you have already mastered that, and wireless signal strength & interference - which are going to be another challenge, more on that later.
Get the camera and the power supply and set it up in the same room as the router, hook it up to you computer and follow the instructions in the manual - make sure the SSID on both the router and the camera match - be aware it is case sensitive, disable ALL wireless security (MAC address restrictions, encryption) on both the router and the camera and then disconnect the cable - if it does not connect with the router at this point, you're going to need to figure out why and fix it - if you have any custom configurations like limiting the number of available ip addresses that the DHCP server can issue or DHCP reservations, disable those also.
Please be aware that the ip address the camera is at may change if you switch from wired to wireless or vice versa - it may have two different MAC addresses and may be issued different ip addresses by your DHCP server.
After you get a basic wireless connection functioning go back and secure it - take things one step at a time.
After you get the connection secured - move the camera back to it's chosen location - it may or may not work, this is where signal strength & interference come into play - if the camera is too far from the router, or there are exterior walls with foil backed insulation between the two, you may have signal strength issues to deal with.