<<< Have tried running ipconfig on base system but it just flashes on and goes off again. Seen to remember this file was called something else in Windows 98? >>>
You need to open a Command Prompt window first and then run IPCONFIG. Alternatively, from the "Run" box launch WINIPCFG
If you normally keep your router running, try powering it off for a couple of minutes and then reboot it. In the laptop, you could try deleting the Profile in your wireless settings and then re-scan and set it all up again from scratch.