Cannot connect Inspiron 1300 to Modem/router wirelessly

This was originally posted in the 'First Time Users' forum - sorry! I have a Dell 1300 Notebook running Windows XP Home Edition. I bought a Speedtouch 585v6 modem/router so I could connect the 1300 to the internet using its 1370 Mini PCI card. Although the signal is strong I just cannot get the notebook to recognise the router. I have eliminated the router as being faulty because I have successfully connected an Acer Aspire 5050 Series Notebook to it. It even works from the bottom of my garden! And I have really eliminated the 1370 card as being faulty because I have connected the 1300 successfully to someone else's network. So I can only presume that the 1370 card is either not compatible with the 585v6 or I have some settings wrong. I do get a notebook/router connection sometimes but never for longer than about 7 minutes, it's almost like a timeout. This is really, to use an English expression, driving me round the twist - I have spend 'days' trying to sort this out. Can anyone help - please?