How to connect 2 computers using different versions of windows 7?

They are on default settings.

I choose my network from a list of available networks.

To enable file sharing between two computers connected on a network. make sure you have the following installed and enabled (with check mark) in your active network cards configuration along with TCP/IP properties.

Client for Microsoft Networks
File and Printer sharing for Microsoft Networks

Make sure both computers are on same network segments (same subnet mask). Give the IP of the wireless router as the default gateway and DNS server for both computers.

Now assign shares and permissons to folders you wish to share with other computer. Use username and passwords for both computers and give permissions to only these users.

I know how to deal with it when I'll see each computer on the other one, but I need is to get there.
And all of what you said is installed and enabled.

I really don't know, and I still can't send ping from one computer to another, I'm still getting the "request timed out" error.
Is them all being the same might be the problem? To what do I need to change it?

I didn't change any settings there. Should I just call my internet provider?

When you connect PC1 directly to the router using a cable, it takes the same IP as the router so that you can log in to the router setup from PC1 and let you configure it.

But I don't think it will put PC1 (while connected to router with cable) on the NAT to enable sharing with other computers (PC2) on the NAT.

I suggest you remove the cable connection between PC1 and router and connect to it using wireless like PC2. Then you can connect to the other computer PC2.

Ideal IP configuration is

Router 10.0.0.1
PC1 10.0.0.2
PC2 10.0.0.3

Default gateway 10.0.0.1
DNS server 10.0.0.1

Try this setup and let us know the results.

May be you can keep the PC1 connected to router through a cable but change the PC1's IP from 10.0.0.1 (router's IP) to 10.0.0.2 to be on NAT.

Whenever you need to configure the router settings you may have to get back to 10.0.0.1 to connect to the router's control panel.