Windows XP & ADSL Hi-speed Internet

Are they all integrated in the same domain/workgroup?.
What services are running in the XP machine?

In the past I saw a network like yours, but I removed Artisoft Lantastic and I setup again the network using only Microsoft Cliet, TCP/IP, etc.
Why do you use Artisoft Lantastic?
About the issue with WinXP and Win98: check if you didn't use the same computer name (both in Windows and Lantastic), the same IP or shares.
I think that your problems are from this combination between Microsoft network and Lantastic.
Give us more details about your network setup.

It sounds like a Browser (not your Internet browser but the browser service) issue to me. Each segment & protocol needs one computer designated as the master browser. It keeps a list of all network resources. If you have multiple computers fighting to be the master browser, no one will be able to use all network resources.

On two of the computers, go into each protocol and disable being a master browser. To get directions for each OS, search google for "master browser" win98, for example. Remember to leave one computer as the master browser. Because of the way the service works, it can take up to 45 minutes for all network resources to show up on the master browser, so be patient.

Don

There are important things you have missed out here, how are you assigning IP addresses, statically or via DHCP and is your modem really a modem, or a router.

First things first, dump lantastic and if you are running netbeui and IPX, get rid of them as well, try to get your windows machines talking to each other just using NetBIOS over TCP (which is all you should need). If you really do have to install another protocol to get windows netorking going (as in file sharing) then add IPX (which also happens to be all that some early games talk, if you happen to be into older games).

Windows XP will always call a browser election if it goes onto a network of older windows machines (and it will always win, being the newest MS offering) so make sure master brower is off and that the XP machine is the first to be turned on, to save having having elections called as each machine is turned on. You could also in such a small network, make use of the lmhosts file to track things, it would not be a hugh task with only 4 machines, just make sure you tell them to use lmhosts before looking for the master browser.

As you have said you set up the ADSL through the network hub, I'll assume that it is capable of doing all the right things and has its own IP address (static on the lan side) and does DNS routing (and if it is not able to do all that, then I suggest you buy a decent quality router!). Make sure that each machine has it's default gateway set up to point to the router and that it also points to the router for it's DNS.

Make sure all machines have unique IP addresses (use winipcfg and ipconfig for win9x and XP respectively to check) and are pointing where you expect them to.

If none of that helps then it would probably require more detail about your network setup to give you a more specific diagnosis of your problems.

And lastly, I'd love to know what your doing on Win3.1 (or is it 3.11, WFW).