You need a USB memory card and the data you want to backup onto your PC needs to be on that card. i don't think USB cards were ever made for the dreamcast though...sorry bud.
I can tell you for the screenshots. You can use the donut system. Not exactly sure how that works on dreamcast. But there is a cube system for it but there was an original one for the DC. I have no idea where it is on the net but its worth looking for. All you need is an internet connection from your DC and you're set. Don't even need an HL. Just a line and a picture to send it once you have the proxy adresss and port number to send it to. The gc donut might work so I'll post that for you since it might.
Proxy Address:
pso.donut.dhs.org
Port Number:
8080
I can tell you for the screenshots. You can use the donut system. Not exactly sure how that works on dreamcast. But there is a cube system for it but there was an original one for the DC. I have no idea where it is on the net but its worth looking for. All you need is an internet connection from your DC and you're set. Don't even need an HL. Just a line and a picture to send it once you have the proxy adresss and port number to send it to. The gc donut might work so I'll post that for you since it might.
Proxy Address:
pso.donut.dhs.org
Port Number:
8080