What you need: (1) BootMyISO, (2) USB flashdrive - any size would do since the .ISO is only around 5 MB in size, and (3) HP Mini 311 Darwin Project current HF4 release
* This is done on a Windows PC
What to do:
1) Plugin your USB stick and run BootMyISO. Just follow the on screen instructions.
2) Access your USB flashdrive and put the HF4 .ISO in it. "HPM311DP_1109CHF4.iso".
3) Look for the "menu.lst" file and edit. Take out all the "#" comment before the lines in the "Test ISO" section. Then replace the name of the .ISO referred to in the file with "HPM311DP_1109CHF4.iso" and save the file. You can rename "Test ISO" to the name you prefer.
(I suggest using Notepad++ for a more intuitive, easier on the eyes editing).
You should now have a bootable USB stick with the release ISO to boot your retail Snow Leopard Install DVD with for your HP Mini 311 and continue with the installation as per usual procedure in the how-to guide.
EDIT: BootMyISO is now MultiBootISO. It's basically the same principle. Here's MultiBootISO's menu.lst file: