The Toshiba Satellite 1900 and 1905 series (P4) laptops are based on a desktop chipset and will only accept one (ONE) mini-PCI wireless card. That's it. One. No other card will ever see a wireless signal. So here goes: the Mini-PCI wireless card is Agere MPC13A-20/R. Toshiba PN ZA2314P04. Dell has an equivalent TrueMobile 1150 Mini-PCI wireless card, which is totally identical. Earlier versions of this Agere card, labeled MPC13A-20 will also work as well, but there's no path to WPA security for the earlier model Agere cards.
This card's drivers are native to Windows XP so it'll be automatically recognized and drivers will be installed by Windows. Of course, this Agere card is an 802.11b card and Windows' native drivers will only support WEP security. However, DELL provides a TrueMobile 1150 Mini-PCI wireless card driver that will allow this card to work in WPA mode - you can download this driver from DELL and your card will be WPA-compatible after installing DELL's drivers. Thanks DELL :-)
The link to DELL's TrueMobile 1150 Mini-PCI card's WPA drivers (Windows XP) cannot be posted here, but Google it, it's "DELL driverID R69905".
To install DELL's TrueMobile 1150 WPA Drivers, first download it from DELL's support site, then un-zip it to a folder named " DELL_1150_WPA" on your desktop, then open Control Panel > System > Hardware > Device Manager, double-click Network Adapters, move to Toshiba Mini-PCI Wireless LAN adapter, right click it, and choose Update Driver. Here's where it gets into unfamiliar territory:
Since the card's drivers are already installed and Windows sees them as the best (most suitable) drivers, you will have to over-ride it. So ... at Update Driver, at the first screen, choose "No, not at this time", click next; at the next screen, choose "Install from a list or specific location (Advanced), click Next; at the next screen, choose "Don't search, I will choose the driver to install", click Next, then, at the next screen, Choose "Have Disk", then use Browse to navigate to the "DELL_1150_WPA" folder that the drivers have been previously unzipped to, select "WLDEL48B" in the folder, and ... there you go. Your wireless card driver will be updated to a WPA-compatible DELL driver and you're ready to rock'n'roll! Windows will recognize your card as a Dell TrueMobile 1150 series Mini-PCI card, but what the heck, that's a driver signature issue and won't cause you any troubles at all.
Not all Toshiba 1900 and 1905 series are pre-wired with wireless antennas, so check and see if there are two antenna wires (leads) at your Mini-PCI slot. FWIW, if your 1900 or 1905 laptop is not pre-wired with wireless antennas, it is super easy to install a pair of screen mounted wireless antennas on these systems: place your wireless antennas behind the screen as with any other laptops, there's already a wireless antenna pass-thru hole located to the right of the video cable connector - so just run the antenna wires thru the pass-thru hole directly into the Mini-PCI slot compartment. And that's it. Just about any Toshiba wireless antenna will do the job.
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The Toshiba Satellite A70 and A75 series will only accept two Mini-PCI cards. That's it. Two. No other card will see a wireless signal, and I've tried just about all of them. So here goes: the two wireless cards that will work on the Toshiba Satellite A70/A75 laptops are Toshiba PA3373U-1MPC and Toshiba PA3416U-1MPC. Both cards are made by Atheros, both are 802.11b/g cards supporting up to WPA security, and performance is terrific. These cards are cheap enough and available enough that there'd be no reason to look for alternatives.
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Special thanks to the fine folks at DELL for the great support - you guys are the best!