This isn't a question, it's a solution that worked for me so I thought I would post it pre-emptively!
I have an old Acer Aspire (32-bit) laptop with an Intel PRO/Wireless 3945ABG adapter from 2008. Having just forced it to upgrade from Windows 7 to Windows 10, I noticed straight away that the wireless was not working (maybe that's why I didn't ever see the Microsoft upgrade option).
I downloaded the Wireless_18.11.0_De132.zip from this page: https://downloadcenter.intel.com/download/25140 then ran the DPInst32.exe file inside the .zip. Nothing much seemed to happen, but on checking Device Manager, the system indicated that the driver is installed but "the device failed to start". I disabled the device, then enabled it - still nothing... getting bored I decided to reboot the machine and start looking for my USB adapter...
Anyway it rebooted, connected to my network and is running perfectly. Not bad for an old Vista machine. Maybe the driver was installed all along and all I needed to do was reboot the machine in the first place. I don't know, drivers aren't really my thing! I thought I'd post this just in case there are other people with similar antique machines lying around.
If it stops someone from getting as annoyed as me, then I've done a good thing