Juno / Netzero or any banner or bar based isp doesn't support alternative OS's directly (BeOS, Amiga, Linux etc). So if your modem is inside your BeOS box the answer is NO. This is because your banner based or bar based isp requires windows period... however.
Workaround: Use a 2 computer network:
Step 1: Add a network card to your computer that has a modem if it doesn't already have one.
Step 2: Install a version of Windows that supports ICS (Internet connection sharing). This can be either Windows 98 SE, Windows ME, Windows 2000 Pro, or Windows XP Home. NT 4 does not have ICS. This will be the machine that runs the windows dependent / banner based or bar based isp.
Step 2: Get a hub or switch to connect the 2 computers
Step 3: Your 2nd computer will be your BeOS box. Add a network card to that. Point your gateway in beos to your windows box that has the banner based isp installed. and BOOM, Beos is surfing the net. you can even add more computers with different OS's the same way. a freebie is that all the banners go to your windows box.. hehehe.. this is the poor man's router so to speak.
many details of networking has been left out and it took me a while to learn networking. stay away from proxy based gateways and stick with ICS because it is Nat based. Nat based gateways are the easiest types to setup. Just stick with ICS since its built into many version of windows.
-good luck, and if u don't know how to do this, ask and maybe someone else will fill in the details, or you can research and fill in the gaps.. enjoy.