Starts a qemu VM with 384 MB of RAM and its BIOS clock set to the time of the clock in the host...
qemu -m 384 \
... with a hard disk connected to hda. The file for hda is lenny.ovl, which is an overlay of another disk file (lenny.img), so any changes in the VM are not saved on the original disk file. You have to use the command qemu-img to create disk files (type "man qemu-img" for more info).
-hda '/home/myuser/qemu/lenny/lenny.ovl' \
This line adds a second hard disk to hdb. The file for this disk is hdb.raw and is in RAW format, created by qemu-img. I use it to save files in it and later I mount the disk file in the host and use it as another mount point to retrieve the files.
-hdb '/home/myuser/qemu/lenny/hdb.raw' \
Boot from the hard disk.
Use the iso file as a cdrom.
-cdrom '/home/myuser/Desktop/CDs/mini-debian-testing.iso' \
No network, but usb enabled (need to add usb devices by pressing Alt+Ctrl+2 on the VM and type "info usbhost" and then add "usb_add host:1234:5678"). Remove the "-net -none" line to have network.
Read the docs to know more about QEMU.
The GUI tools that I posted before - qemu-launcher and qemulator - handle all this options for you with a GUI.
Here is a link to a video file with qemulator: http://qemulator.createweb.de/conten...al&typ=richdoc
Try it (or qemu-launcher), it's more simple and less confusing for the start.