First of, this has been asked and answered many times, did you try to search for "install vista from usb stick" in google? But anyways let me give you the answer, I'm in a good mood today.
On a system already running Vista (there's no way around it unless you got a WinPE boot disk version 2.0 or 2.1) and put the stick in your PC. Open a command box (start -> run -> cmd) and run the following commands:
# diskpart
# list disk
PAY VERY GOOD ATTENTION HERE AS YOU MIGHT WIPE OUT YOUR 2ND OR ANOTHER HARD DRIVE THATS NOT YOUR USB STICK!
DISKPART> list disk
Disk ### Status Size Free Dyn Gpt
-------- ---------- ------- ------- --- ---
Disk 0 Online 149 GB 0 B
Disk 1 Online 3836 MB 0 B
(in this example disk 1 is the usb disk, you can check which disk in the list has the size of your usb stick, my stick is 4gb.)
# select disk 1 (be sure the disk you select is your usb stick!)
# clean
# create partition primary
# select partition 1
# active
# format quick fs=fat32
# assign
# exit
After this navigate to the usb stick via "my computer" then unpack the ISO you made to it. You can also copy the files from the vLite workdir to it.
I hope this helps, but next time please use the search