Well simple file sharing is far from perfect. There are a couple of things for you to try (but obviously first make sure that the file and print sharing is allowed in everyones window firewall--or turn it off temporarily while you test these ideas out) First of all a lot of times on computers using simple file sharing before you can share an entire drive (like a cd rom or the root of a hard drive you need to share a folder with at least one document in it). You are probably saying to yourself now--I should not have to do that, it should work the way it is configured. And you would be right, however this is a problem with simple file sharing. So make sure that the a folder with at least one file is shared on the hard drive of the shared cd rom computer. (make up a test folder and a word doc if you have too)
If that does not get it make sure there is at least one shared folder with each computer in the same way. Additionally, if you are using simple file sharing you usually don't see the everyone full control options because that is in the permissions level of the security without simple file sharing. With simple file sharing you usually only see "share this file on the network" with a check box, and "allow network users to change my files" with a check box. If you want to use simple file sharing all around then verify it is selected from windows explorer (not ie) tools menu-folder options--view tab.
If still having problems then you can try turning off simple file sharing, but then you will have to be extra sure you go into the extra permissions level you can see without simple file sharing and verify everyone full control is selected.
On an earlier question I answered for you regarding your usb adsl modem you replied that I provided know info--which basically was get a standard modem. Well there really is a functional solution with one problem--I did not type it out before because it is a long explanation, but I will provide it here.
If you connect you usb dsl modem to the computer you can then able ics (internet connection sharing) and then point the share to the ethernet card. This will server out an ip address via your ethernet card. Then the ethernet card needs to be plugged into the wan port (sometimes labled internet) of the router. The router needs to be configured to dhcp (sometimes labled obtain auto). Here is the catch. The lan of the router can not be on the same subnet as the lan. Hence if the computer is serving a 192.168.1.x address to the wan port the lan has to be on a different scheme. So you will need to set up the lan side as 192.168.2.x where x could be 1 or whatever (less than 253) Then turn on the dhcp of the router and connect your two computers to the lan ports either hard wire or wireless. You will have to make sure each of these two computers are set on dhcp. Otherwise you will need to give them static addresses in the same subnet as the router e.g. 192.168.2.10, 192.168.2.11 A subnet mask of 255.255.255.0 is fine for everything. If you give those two static addresses you will have to enter public dhcp address and don't forget to put in the gateway which is the lan side of the router.
Make sure the router is getting dns address info from the ethernet on the computer with the usb using the ics. If not then you will have to fiddle with the ics to make that happen. Or you will have to enter manually.
Ok here is the rub and this is definitely important because you are talking about sharing in this question. The computer that is hooked up to the usb modem is on the wan side of the router and the other computers are on the lan side. Furthermore, by router definition the wan side is in a different subnet than the lan side (that is because a routers job is to hook networks of different subnets together) Therefore, they will not be able to share files (or cd rom drives). However, the two computers on the lan side will be able to share files.
This might be able to be overcome by putting in some sort of static route--but I am not sure if that would work, and if it would I am not sure of how to do that.
I have done this exact procedure with someone who had a pc card in a laptop for cell phone wireless and we hooked it up to a router in just this manner and it worked fine. Again as expected the computers on the lan could not share with the laptop on the wan.
Ok --maybe this helps or not, but I felt badly for not taking the time needed to type this option out for you before
good luck