Haven't read through the whole thread just the first post. All I wanted to say is that you will need to have another wireless NIC for two simultaneous wireless connections. The destination IP address will determine what NIC will be used to reach its destination (Both networks need to be on a different subnet).
For internet connection, Windows will automatically use the connection with the lowest metric which is normally the one with the most amount of bandwidth.
True, if two simultaneous wireless connection networks were truly required.
But subsequent information by the OP reveals that the real situation is that the ISP-provided Netgear DGN1000 DSLmodem+router (N150) is only 10/100 on its wired side. And he turned off wireless capability in the N150, thus providing only DSLmodem plus 10/100 wired capability for anything connected to that device.
However he wanted faster inter-device capability for the wired/wireless devices within his LAN, so he bought a second device he thought would provide that capability, i.e. a Netgear WNDR4500 router (N900) which supports 10/100/1000 speeds on wired connections. The wireless capability of the N900 was enabled, so all wireless connections went through this N900.
And the N900 itself was "strung wired" off of a wired port on the N150, so he now had TWO routers (arranged linearly, not two separate subnets talking simultaneously to two separate NIC's in his PC) that any device had to go through. He thus did get 10/100/1000 speeds within the devices connected "wired" through the N900, although that would of course only not be true for any devices connected wirelessly through the N900 where only 811.n speed would have been possible, and very likely less that maximum in the real world for devices not nearby the N900 router.
So his needs really do not require multiple routers. One N150 10/100 router would do fine to provide Internet access for any device needing it, with a "gigabit switch" (not a second router) providing perfectly acceptable 10/100/1000 internal LAN connectivity if all devices connected "wired" were connected to the switch, and the switch was itself wired connected to a wired port on the N150 router. Everything would be satisfactory if no wireless capability were needed.
But if wireless capability is also a requirement, then simply adding a wireless access point (again, not a second router) would be perfectly adequate. A device like the Netgear WN604 provides 811.n along with a 4-port 10/100 wired switch, although if that 10/100 speed had been acceptable then the wired ports of the N150 could be used directly (and the N150's wireless capability could have been enabled). Again, one router (the N150), 811.n wireless, and 10/100 wired capability through the WN604 and N150 router, ability for any device to get to the Internet if needed, and a 10/100 switch on the WN604 for inter-device speeds for devices connected wired to the switch. And all devices can see each other.
Or, if higher inter-device speeds of 10/100/1000 for devices connected wired are truly desired, a higher speed wireless access point (again not a second router) with 4-port 10/100/1000 wired switch functionality such as the Netgear WN802 would be the ticket. Now you again have 811.n wireless, plus 10/100 speeds for devices connected to the wired ports of the N150, along with 10/100/1000 speeds for devices connected wired to the wired ports of the WN802. So now you have one router (the N150), 811.n wireless, and potentially gigabit connectivity for devices connected wired through the WN802.
Again... only one NIC is needed in the PC and it can even be purely wired, connected wired to the N150 if the NIC is 10/100. If the NIC in the PC is gigabit, it can be connected wired to the WN802 in order to be able to communicate to NAS and other LAN devices also connected wired through the WN802. So only one router is needed, and all wired/wireless devices connected through the WN802 will appear to be "wired attached devices" when viewing the table of attached devices back n the N150 router.
One router, and one wireless access point (which includes a built-in 4-port switch for wired devices).
That turns out to be the story.