Comment 1 for bug 623030

You should be able to remove the boot entry by running bcdedit in the command line, and using the delete flag, as described at http://technet.microsoft.com/en-us/library/cc709667(WS.10).aspx ie use "bcdedit" to see the entry listing, see the id for the UNetbootin entry, which will look something like {24972-29572-...}, then "bcdedit /delete {24972-29572-...}" (substituting in the id appropriately) to delete it.

Also, what version of UNetbootin did you install with, and is this Vista install 64-bit or 32-bit?