Cable, DSL, or phone?
I have experience with basically just cable modem right now with WindowsXP. There is no log on, you just run Internet Explorer and you are in. E-mail requires a user name and password, but I do not know how it would work with two user accounts. Likely you could set it up for both, but if you check for e-mail on one account, it will not show up on the other unles they do not keep them separate or Outlook has an option to share the e-mail between users.
I did it the less confusing way. I just set up a new computer for everybody in my house. My Ex has her own at her appartment, I have one, and I have three others to split between the kids (my youndest has not figured out computers yet, but he is trying). They are 2, 4, and 6. I also use the computers for LAN parties.
AMD Phenom II x4 945 3Ghz | ASUS M4A77TD | 2X WD 1TB SATA 2 hard drive | 2x2GB Corsair XMS3 | nVidia GeForce 8800 GTS | ATI TV Wonder Theater Pro 550 | Antec P-160 case | Antec 650w Earth Watts | LG Blu-ray Super Drive | LG DVD RW | Windows 7 Pro