There are a few generic shapes in Visio - on the Office Equipment stencil.
If you have Visio 2002 or 2003, you can also use the Search tools to look
for more shapes on the Visio downloads site :
In 2002, choose FILE then FIND SHAPE from the menu
In 2003, use the Shapes search section in the stencil window
Any shapes that you will find here will be pretty generic. You can find
many shapes on the internet by searching for 'Visio shapes' on any internet
search engine, and you will find many free and inexpensive Stencil packs of
various descriptions.