Hello and welcome RobertWK. To answer your internet question, you can use XDP as a browser. It is the current browser of choice. The question is, what is your online set-up? You would need one of the following to get online.
a.) A dial-up ISP. This does not allow you to connect to all of the games as far as I understand.
b.) A Raspberry Pi with DreamPi with a USB modem. Recommended as #1 way to connect and easiest.
c.) What some of us call "Netopia" set-up. This takes a bit of hardware, a bit of setting up and does not connect to all games.
d.) DC-PC server setup. This does not allow you to connect to all of the games and takes a bit of know-how including using WinXP, Ubuntu (or other Linux distribution), a modem, and virtual machine software.
Guides exist for all options but the DreamPi is the latest and by far the best method. It's really simple and there is a really good video tutorial on Dreamcast-Live. This just "works" while the other methods had limitations and take a bit of setting up on the PC end.