ESXi 4 can procedure can be found here
Updated for ESXi 3.5 update 4
This is ridiculously cool. I have a quad core motherboard with 8 gig of RAM that won’t install VMWare ESXi (it’s an ICH8 board and only ICH7 and ICH9 will work), but I’ve been hearing that you can install ESXi onto a thumbdrive and run it on boards that wouldn’t work otherwise. Most instructions are for windows and, being the windows dude that I am, I decided to tweak it for linux. First, you’ll need a linux box and a 1 gig or larger USB drive. Download the ESXi ISO and then mount it in linux like so
mount -t iso9660 -o loop VMware-VMvisor-InstallerCD-3.5.0_Update_4-153875.i386.iso /mnt/esx
Now we’re going to write the installer file to the thumbdrive. I’m assuming the thumbdrive is /dev/sdb
tar xvzf /mnt/esx/install.tgz usr/lib/vmware/installer/VMware-VMvisor-big-3.5.0_Update_4-153875.i386.dd.bz2 -O | bzip2 -d -c | dd of=/dev/sdb
This will take a little bit, but once it’s done you’re good to go. pop that drive into a USB boot capable board, configure iSCSI storage and emulate away!