http://www.tomshardware.com/forum/243423-32-image-flash
another link http://www.boot-land.net/forums/index.php?noref=1&showtopic=7739
http://unetbootin.sourceforge.net/
This operation assumes your machine can boot from a USB enabled device. Check your BIOS to make sure. You also MUST have a DVD copy of Vista to install the source files from the DVD to a USB flash drive:
1. Insert your USB flash drive and enter the following commands:
(please note this list assumes that your USB flash drive will be seen as disk 1. To confirm that it is type “list disk” after you’ve entered the DISKPART command) Otherwise you may wipe a different drive (such as your hard disk drive!)
2. Type:
diskpart
select disk 1
clean
create partition primary
select partition 1
active
format fs=fat32
assign
exit
At this point your USB drive is formatted. DO NOT format the drive from within Windows. You MUST have a DVD copy of Vista to copy the source files from.
The final preparation step is to copy the installation files to your flash drive, this can be done by running the following command:
(Please note D: is the drive letter for the source files and E: is the drive letter for your flash drive, if they are different on your system you need to change them accordingly).
Exit DISKPART. Type:
xcopy d:\*.* /s/e/f e:\
Thats it, configure usb device as primary boot device in your bios and install.