OK, the best way to is to forget about the USB ADSL modem.
Get a wireless ADSL router/firewall all-in-one. By curious coincidence, there is one reviewed in Issue 2 of Home Computer Magazine, a free PC magazine I?m involved in (shameless plug, I know). You can read the review by getting the mag from home computer magazine
It?s a great bit of kit ? we bought one ourselves!
What it will do is plug into the telephone line and provide a permanent gateway to the internet, and share that with the other PCs. The laptop can access it without any additional hardware.
The PCs will require some sort of connection. Now it sounds like one PC is already connected via wire to the ADSL modem and the phone line, so proximity on one of the PCs shouldn?t be an issue. In this case you can use the wire part of the hub (the router mentioned can take up to 4 PCs plugged directly in as well as providing wireless networks ? you can mix wired and wireless networks without a worry) with the network cable that is supplied with the router. This will save you buying a wireless ?card? for that desktop, and will give you better network speeds.
For the remaining desktop, you just need to buy a USB wireless networks device. There are lots of different options here, but check out any site like Dabs or Simply and you?ll find one. If you need more help on this, let me know.
Lastly, ensure you set up the wireless correctly. It is a bit difficult, but you might like to read the Broadband tutorial in issue 2 of the magazine, which starts to cover the basics and the next issue, published in a week, has the second part which specifically covers wireless network setup.