You need a converter box, LIKE
this one.
Im sure there are many that would work. You could use a vga splitter, then run one to the vga monitor, and the other to a converter. BE mindful of the specifications of such devices; not all are compatible with all resolutions, and not all provide multiple outputs SIMULTANEOUSLY.
EDIT: From the specs of the product linked to above:
Output: Simultaneous (with VGA Splitter Cable) on VGA Monitor and to: Video Monitor/Projector, TV, VCR, etc