Change the type to Linux. You can do that in fdisk or cfdisk.... you apparently already know how to do that since you partitioned it
I am guessing that the dm-0 crap is the lvm device name... but I dont know lvm, and you said it can be dumb as a rock so lets not use it
# Create a filesystem on the device
# Mount it so it is accessable now
mount /dev/sdb1 /mnt
# Make it keep working when you reboot.
# Add this line to /etc/fstab
/dev/sdb1 /mnt reiserfs defaults 1 2