ok gurus, dont murder me for asking this but i have a question that google has failed to answer (or maybe im not typing in my query correctly ..idk). im making a bootable USB with 3 or 4 distros. im using unetbootin to load them. but i have not found any plain-as-day simple as 1,2,3 instructions on how to edit the syslinux.cfg file for persistence. is there not some kind of code for this? any insight will do. thanx

I've no idea if this would work but it's a novel idea and shouldn't damage anything.

Try disconnecting your internal drive. Boot from a live CD, say, Ubuntu, with the USP drive plugged in. Run up GParted, can you see the USB drive? If so, set up your partitions and load them up one at a time. The boot loader should be written on the front of the first partition and allow access to each distro. Hmmm... I'm not sure if this is too simple to work but give it a go and report back.

This would mean that with your internal disk reconnected, you'd only boot whatever was on that drive unless you hit <F9> or whatever to give you the boot menu on your system. Select USB to give access to the multiple distros.
Ta Dah!

Whaja mean you're building it on a laptop/netbook and you can't get access to the internal disk!!
Build it on a desktop box then you can use it on either providing you can select the USB source from the boot menu.

Play Bonny!

I doubt you can easily get persistence using unetbootin but it may be possible. Usually you can't use the casper file for more than one install at a time. Start a pendrivelinux.com for most of the current ways to proceed.

There are basically two ways to make persistent installs.
One is to use the fat format and some application to put either the iso or parts of to a usb.

The second way is to use the usb just like a normal install. You partition it and format it in some linux format and install. This way would allow you to use your flash like a normal drive. Be careful though. The install may not be clear on how grub will be installed.