What do I need for office router/switch

What do I need for office router/switch
I don't know where to put this so I will start here. I have a host computer running XP that we keep Quickbooks Pro/Premier on and then we have 3 other computers running XP & Vista that connect to it. The host has the main programs on it and we pull off it to do Quickbooks. Everything is stored on the host.
I want to hook up the 3 computers so the will run the fastest they can to the host and to each other in a hardwired LAN. All of the computers have gigabit dual ethernet on the mother boards. We use ATT/Yahoo DSL as our internet. I am not really that worried about how fast the DSL is because I know it will be dependent on ATT, but I do want to wire these as fast as possible between each other. Right now the way they are wired they seem to be slow.

The ATT modem is connected to Sonicwall with 4 ports in the back of it and the 3 computers and the host (total 4) fill the 4 ethernet ports on the back of the Sonicwall. I want to get rid of the Sonicwall and get something cheaper without the subscription service.

What do I get. Do I get just a router and hook it up like the Sonicwall or do I get a router and connect a switch to it and hook all the 4 computers to the switch (which I have been led to believe that a switch is faster than a router). Or do I do it a different way. I am thinking about getting something like a D-link gigabit dual channel wireless router and hook the 4 computers to the back of its 4 ethernet ports so I can add wireless printers in the future. This might be a waste of money since I don't have any wireless printers at this time.

Please advise which is the best/fastest way to hook up all 4 computers together so they play nice together. The host only gets updates from Microsoft and Quickbooks on the internet, but we use the other 3 computers on the internet looking stuff up and email all the time. Mainly, I want Quickbooks to be almost instantaneous when we look up invoices and financials etc from the host. Please any suggestions on what equipment to get and how to hook it up. Also would teaming two ethernet connections from the host computer to the router or switch be faster. Please advise. And thank you in advance.
Aranon