The only big ISP's I know of that oficially support multiple users are AOL and Earthlink. Since I refuse to contaminate my computers with AOL, I've added an Earthlink account (roaming and backup access for me, full time access for another family member).
Their policy is that if you're both on at the same time, they charge $1.00 / hour, rounded to the nearest minute. I also get some decent discounts (USAA + Sprint). So far they seem OK -- I was getting 4-5K/sec download speed.
Interestingly, if I'm connected to both my DSL line (via Ethernet part of my Linksys combo PCCard) and POP (via modem side of Linksys), my Win 98 laptop seems to only use the modem. At least it looks like I won't have to reconfigure and reboot to change between modem and DSL.
Note for tjsinclair -- I've given my friend the pitch for the SMC Barricade. He's interested in the print server.
Tony