Simple, unlike Fut1i1ity, who had strange problems (probably with an old kernel), this works like a charm with DD's script. I have done this several times and no issues along the line of Fut1i1ity's.
Now that I have this all running is there a way to make it where all the EFI, etc. are on a USB flash drive?
You mean from the DD script in Leopard and create SL install w custom kexts? No. Snow leopard does system level commands such as mkext rebuilding differently and is incompatible. Once one is in SL they can mkext rebuild with mkext maker for SL. Also once in SL, DD's script can be used. At least this is what I have been told.
Also, when SL disks come out we would be able to install directly from the DVD.
Already answered yes on that. And obviously as I said before you cant install snow leopard kexts on leopard.
Can the script be setup to install the necessary parts to a USB drive?