DSL Router or Modem

setup a DHCP scope on the 2000 Server and have your client machines use DHCP to get IP address.

to add configure DHCP options 03,06 router & DNS

If you have only a switch, you'll have to use your server as your router.
Your server has its DSL modem installed. Whether it's internal or external is unimportant.
Your server also has a NIC hooked to your switch.
You will need to set up your internal network with manual IP addresses or allow your W2K server to issue DHCP addresses to the hosts plugged into the switch.
If your desktop hosts can see the server on your local network, all you need to do now is enable Internet Connection sharing on the server. Have a look here:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;237254
This is Microsoft's article on enabling ICS.
Once ICS is enabled, then you go into the IE on your desktops, click Tools, Internet Options, go to the Connections tab, and in the lower right click the LAN settings button. Your desktop should be able to auto-discover the ICS server, but if not, you'll need to add it as your proxy server.
That should get you most of the way there.

Okay, now that that's said, let's add one more option. Go to Walmart, OfficeMax, OfficeDepot, BestBuy, CompUSA or any of a host of web retailers, spend $50 on a broadband router, hook it up to your DSL connection, and let it issue DHCP addresses and allow all your hosts to go to the Internet without using your server as a proxy.

If your DLS modem is internal and has no Ethernet connection, then you'll need to spend a bit more and buy a router with a built in DSL modem.

Hope this helps some.

Hi,

You do not offer enough information to answer this question realisticly. Does the DSL modem have a static or dynamic IP address? Are you using the 2K server as a proxy server? If not, why do you want the workstations to connect to the internet via the server? What Opsys is on the workstations? I have no idea as to how your server is configured or your network. I can only make guesses.
Questions aside, and thinking you are not using the server as a proxy server or that it does not have AD, DNS, and/or DHCP configured, here is my approach to your problem:
If for no other reason than for added security, I would replace the switch with a NAT router. The router can be configured to do the DSL login for you and each computer has instant access to the Internet. This also eliminates any problems of a dynamic ISP IP address on the modem. The router will do the translations for any computers connected to it regardless. Configure the router to be the DHCP server and assign the internal scope that you wish to use. Assign an IP address to the server that is within the IP range of the router LAN settings and outside of its DHCP scope to eliminate any possible IP conflicts on the server. A server with a dynamic IP address has its own issues aside from this. Set the router LAN IP address as the gateway for the server and set the DNS servers as per your ISP DNS servers. The DHCP service on the router will pass along the ISP information to the dynamicly assigned workstations. Problem solved, unless you have Win 2K and/or Win XP workstations, or if the server has AD installed, or if DNS and/or DHCP are installed without AD. Should this be the case, there are other issues to consider. email me should this be the case. Even with these considerations, the workstations will still have internet access anyway.