Dual Connection Issues
On a dual connected laptop (WiFi and wired) the WiFi will often "win" because it comes up slower and it's DHCP settings come in after the faster wired LAN connection. - http://superuser.com/questions/237892/why-is-my-laptop-favoring-the-wireless-connection-over-my-lan-connection
Free WPA software W2K - These guys offer a free WPA enabler for Windows 2000 for people who want half-decent wireless security in W2K
http://www.wirelesssecuritycorp.com/wsc/public/WPAAssistant.do
WiFi Public / Private / settings
Network and Sharing Center
Vista: Click "Customize" beside network name to change from Public to Private. WiFi and wired.
WiFi speed in Win10 (probably earlier too)
It's harder to find on Win10
netsh wlan show interfaces
ncpa.cpl - brings up old school interface
WiFi per user in Win7 - Network and Sharing Center. Manage Wireless Networks. Profile Types. Default is all users, but you can select per-user. Then you have to remove old WiFi network, recreate w/settings.
http://www.howtogeek.com/howto/43782/how-to-enable-user-specific-wireless-networks-in-windows-7/
WiFi Connections List (Vista, ...)
The term is "Manage Wireless Networks" - under Control Panel. This is where to delete bum WiFi network connections for rebuilding.
Intel PROSet/Wireless Tools
Control Panel. "Profiles" button, from there to delete broken profiles. Don't use Windows built-in tools.
Start Menu - All Programs - Intel PROSet Wireless - WiFi Connection Utility for joining networks.
Misc Hardware Notes:
Dell E5540 - Has a BIOS option to enable WiFi and Bluetooth. And a physical switch on the left, right by the power jack.
Guest WiFi - isolation from regular LAN from an AP (not a router) is difficult / impossible (VLAN). From a client on Guest WiFi, the LAN "is the Internet" - http://superuser.com/questions/592121/guest-wifi-mode-on-a-secondary-router
WiFi N Theoretical Speed: You MUST use WPA2 authentication with AES encryption only. default channel is 20Mhz, which allows for a transmission rate of 150Mbps. But on devices that support it, you can have wider channels, such as 40MHz (300 MBps), but don't bother, 40MHz is impractical, too much interference.
Troubleshooting hint: Apple (AKA iPhone) does NOT allow 40MHz channels on 2.4GHz. If an iPhone works and a laptop doesn't... maybe 40MHz channels (which are a bad idea on 2.4GHz) should be disabled.
WiFi Roaming from AP to AP (with same SSID, etc.):
On consumer gear, this is basically up to the client. And connections do drop during the handoff (I think this would kill file transfers). Ubiquity, Meraki, and other high end gear broadcast the same MAC on all APs and then manage which AP will service the connections through back channels - http://arstechnica.com/civis/viewtopic.php?t=1256649 - terms would be Layer 2 and Layer 3 roaming.
Preamble - Short vs Long: Long is more compatible. Short is "usually compatible". When in doubt, and a smidgen of speed isn't going to count, use long. For some reason D-Link defaults to short.