Hello Zackyjack, What you want to do is possible but isn't easy to setup and maybe problematic, If you are using Xp you can setup connection sharing on your main computer which would still have to be plugged into the Wired router, And then you can connect to your wireless connection on your computer using an Ad-Hoc Mode that your software will have on the laptop,
for this to work you will have to have wireless working on your laptop e,g, Internal Card PCMCIA/USB Adapter. you will then be able to connect to the Wired computer, I havn't tested this for a while but when you setup the Host(Computer being shared) XP has a system that can create a setup disk that you can run on your other computers that you want to use the share on.

Beware that Firewalls will most likely stop your other computers connecting to each other so switch these off whilst setting up the connection and then add these once it is working,

That said even though something is possible I would go for the something like the Dynomode R-ADSL-C4W-G1 54Mbps Wireless router this isn't the most expensive in the world but would have everything you need, You can still then use the USB adapter you got from the shop and then not have to use the cable from the router to the computer. OK here comes the grtatuitous bit we do happen to have them Allwireless.co.uk Wireless Networking and Home Automation for Home and Business Dynamode 54 Mbps Wireless router R-ADSL-C4W-G1.

I hope this helps a little in short you can do what you asked but i personally would go for option 2.