I need to make Windows 7 STOP disabling the wifi adapter when the wired LAN is connected

In my case the problem was a Windows service called "Wireless_AutoSwitch." I have no idea how or why it was installed but disabling it fixed the problem.

What kind of adapter does the Dell have?

For instance, here you can see that the "Intel® PROSet/Wireless" has software which can disable the WiFi when a LAN cable is connected. You need to disable that option there too.

So look in the system-tray for such software and look for that option.
(Or tell us the make/model of the WiFi adapter and we can look for it too :)

Edit #1: (more options to try)
According to this your "Intel(R) Centrino(R) Advanced-N 6205" can come with the "Intel® PROSet/Wireless Software". But if you can't find it in the system-tray or "Installed software" i guess it's not at fault. I doubt there is a setting in the driver for the LAN-adapter but it never hurts to check. Also check the settings of the WiFi-adapter for such option. Also remove the check here of your WiFi adapter. It might be that Windows shuts it down when a cable is detected.

And here is another option to check. You need to set the "Power Saving Mode" of your WiFi adapter (in Advanced Power options) to "Maximum Performance".

Edit #2:
I guess you mean by you disabled it in the BIOS you did the reverse of this:

• Go to BIOS by press F12 during reboot.
• Power Mgt ==> wireless radio control
• UN-check the "Control WLAN RADIO & Control WWAN RADIO"
• Reboot the laptop.