USB to reboot a Macbook Pro

Hey guys! I'm new to the community I would like to say hello and thanks for helping!

Now let me explain what I would like to do. Basically i have a .dmg (image) file of snow leapord on a macbook pro and I would like to use my 8 gigbyte usb flash drive to reboot the mac. I was wondering if this was possible because i'm sorta new to the mac's cause on pc its fairly simple. If anyone can give me some tips on this that would be awesome. Also when I double-click on the actual .dmg it tell's me to mount it onto a DVD-CD then attempt to the only problem is, is that I don't have a cd that stores 6.6 gigs So if anyone could help me out with this matter that would be awesome thanks again guys.

P.S: I will be checking back on this thread in about 2 hours, I got class :s Thanks again!

G'day and welcome to the forums.

Got a better idea ~ use the Snow Leopard disc to boot from. You do have the disc one imagines?

Thank you, I litterally have the .dmg file on my laptop I had it on a usb and transfered it over to the actual laptop, so now I was wondering if whether I can actually boot the mac with that usb through disk utilities or something, Honestly I'm doing a favor for a friend so im not too familiar with how the mac works.

Well if you do not have the disc that is illegal so I guess you will get little help here.