If you do a File|Save, excel saves to the same location.
In xl2k and higher, file|saveAs tries to save to the same location as the
workbook that was opened.
In xl97, file|saveAs tried to go back to your default directory.
I find that it's easiest to let excel do what it wants.
But in xl2002, you can add your favorite folders to the "save in" (left hand bar
in the file|saveAs dialog) by selecting your folder and then Tools|add to "my
Places".
In xl2k, you can use an addin from MS:
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q253338
INFO: Office Developer Samples and Tools Available for Download (Q253338)
Scroll about halfway down. Might make your life a little easier.
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Another option in xl2k:
I've added a shortcut to my favorite folders so I can click on "favorites" and
then click on the shortcut to my favorite folder.