Boot able means that there is an OS of sort on the CD/DVD and the bootstrap tells it to load the OS at startup.
If it is not the whole OS but just the SP2 update file , then there is Nothing to Boot.
Otherwise you need the original Vista DVD, and you first slip stream the SP2 file into it and create a Bootable Vista SP2 DVD.
http://www.vistax64.com/tutorials/230249-sliptream-vista-sp2.html
If you use it for upgrade an exsiting installation it has to be the type that is compatible with the current installation.
Otherwise you need a new key, and activate after you use this DVD.
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