Re: can i combine my internet and file sharing with one wireless device?

You will need a Broadband Wireless router. Some allow wired and wireless connections to the network. If you have NIC cards in the older PCs, you wont need to buy wireless adapters for those. You can configure each PC to access the Internet on its own or thru one of the PCs. Wireless routers are about $70 US, adapters a bit less.
Configuring the router and each connection can be a challenge if you are not an IT person.