Since I recently switched from dial-up to SBC DSL, I'll try to help. The modem is offered in two flavors: single
computer, or multi-computer if you want to network(this unit is good in that it includes a hardware firewall).
The multi-unit modem is $50 extra. There should be no
problems using Windows and Mac(Linux, you'll have to do your own tech support). The $29.99 price is for the DSL
line and presumes a LAN setup. I had to uninstall parts of that since I use a dual-boot Win/Linux standalone.
I'm not sure about using Mac 8.6(even 9x is considered
old nowdays).
Changing ISPs is traumatic until you have done it a few times. Didn't like Yahoo at first, now I like it better
than the ATT I changed from. And Earthlink before that.
Just be patient with configuring it to your needs. Took me a while to make my Mozilla browser/email program access my Yahoo mail accounts.
After 1 year, you have no obligation to SBC/Yahoo. If
you don't like the new price, move on. Prices will probably be cheaper then, though. Hope this helps. chuck