Ive been reading up a bit on USB booting. Theres a variety of reasons to do this. Some people make their own toolkits that they want readily available - some simply want to boot WinPE. Now that WinPE 2.0 comes with Vista DVD's and the WAIK, it provides for a ready easy way to make your own set of tools.
Ill leave aside the coolness of ImageX and packaging up your own custom image - though you can easily play with this. You simply need a copy of the WAIK which is freely available from Microsoft.com/downloads, install it and you have the necessary tools to open up the boot.wim file and add your own stuff in.
So how to get it booting you ask?
Several easy steps.
1. Find a shiny new USB stick or one that you have backed up the data from
2. Format it as NTFS
3. Load up an (elevated) command prompt window
4. Run diskpart.exe and then set your drive and partition to point to the stick. Make sure you set the paritition as Active.
5. Theres a tool in Vista called bootsect.exe. Cant find it? Its on the Vista DVD itself in the Boot directory.
6. Run bootsect /nt60 <drive letter of your USB drive>
7. Copy over the Boot directory and bootmgr from your Vista DVD to your USB drive
8. Create a directory on your USB drive in the root of it called "sources"
9. Copy over the winpe.wim file from your WAIK directory and drop it into sources. On my machine its located at C:\Program Files\Windows AIK\Tools\PETools\x86
10. Rename winpe.wim to boot.wim
Youre now good to go and have a bootable USB drive with WinPE