Upgrade os x 10.5.8 to 10.6 - early 2008 macbook

I have a Macbook (early 2008) running with OS 10.5.8. My questions:

1) I have seen people upgrade either from 10.5.8 to 10.6 or directly to 10.7 by using a usb boot media. Since my dvd reader does not work I want to use the same method. After doing some research on the internet I figured that the usb drive must be formatted properly (creating a partition with proper indexing type). I did follow the instructions as given (confirmed by several users). By using both the disk utility and the carbon copy clone I created the bootable usb drive and booted my mac by pressing alt (option) key. Bootable usb appears and I choose it as booting drive. After a few seconds a prohibited sign appears on the screen and mac skips the boot from this usb and boots into my 10.5.8 without giving any error messages.

People say this probited sign means there are some files missing in the usb drive I created. I tried several options but every time the same sign and I can't boot into my 10.6 installation. Any suggestions?

2) Each time I used a 64 GB usb 3.0 flash drive. Do you think it could be related to the usb 3.0 compatibility?

3) I tried almost every combination to reset boot sequences such as alt + cmd + p + r. Pressing "c" does not do anything on my mac so I don't see the apple logo when I keep pressing the "c" key.

4) When I start the 10.6 installation directly from the running 10.5.8, installation starts but it does not move after 1-2% saying 45 min. left all the time. First time I tried, I got the message that my computer must be restarted and the installation would continue after reboot but it did not! After running repair disk permissions, found some errors and fixed them, it did not complete the installation, 45 min. left as message below on the installation bar, let it run for at least 4-5 hours, nothing happened.

5) I tried using a spare HDD but did not boot again, showing the prohibitation sign at the center of my screen.

I would appreciate any suggestions.