There's a variety of commands that will fetch the information you're looking for. They're all listed in the documentation for label.dll. Here's what I use in my label:
LabelText "C: [diskinuse('c:')] of [disktotal('c:')]\nG:
[diskinuse('g:')] of [disktotal('g:')]\nRAM: [meminuse] of [memtotal] \nCPU: [cpu]\nIP: [ip]"

The stuff in brackets is the data that's fetched. the \n is a line break