First up (off topic), since this appears to be a 2nd-hand computer, I'd do a
fresh install of Windows.
You don't know what's been on it (in terms of viruses, malware etc), and
there's also an issue of the legitimate transfer of the licence for Vista.
Did you receive all the disks etc with this computer, along with the CD-Key
code (sticker is probably attached to the case, or with the
documentation/disk containers)
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Anyway back to the question.
Generally the 'save/download' location is set through whatever browser
you're using. e.g., in Firefox you go to Tools/Options, and in the "set
download location" section it gives options to save to a particular folder
all the time, or it can be set so it will prompt you where to save the file.
Other browsers would have similar options.
I expect it's the same with office suite or similar such application like
Open Office or MS Office. Usually the save routine (where saving a file
for the first time) will prompt you to save where you want to, and it might
default to the "last saved in" location, or to a specified folder as set
through that application's options. In any case I'm sure it's not actually
something you can set in Vista itself.
If this is not the sort of thing you're asking about, can you be more
specific?