Help-Mitsubishi monitor

[EliotE@aol.com]

Is there anyone using a Mitsubishi Diamond Scan monitor out there?

I've stumbled across a used 21" built in 1988, but I don't know how to hook
it up.
There are 5 round connectors on the back, labelled: R,G,B,HD,VD;
as well as a 15 pin connector (which I tried on my ATI Mach64 with no
success).    
Do I need a special video card to connect it?

I've tried to find a number for Mitsubishi tech support also, to no
avail.-help!