Can I connect the LAN Ethernet card and WiFi at the same time through the single ADSL2+ router network?
If your router provides wifi functionality then there's no reason why you shouldnt be able to connect two or more devices to it using mixed wifi or ethernet. Of course, you'll be limited on the ethernet side by the number of ports on the router, but wifi is limitless. This would be the expected behaviour anyway, if it is indeed a *router*. However, I know some ISPs provide a simple interface device instead - usually either USB *or* ethernet can be used with those, but I haven't heard of one that would provide ethernet or wifi without it being a proper router.
I assume of course that you're using different computers, because trying to use the wifi and ethernet to a single router from the same computer would probably result in some kind of a parallel flux capacitor discharge, resulting in a black hole and possibly time travel... ;)