Set desktop to 640x480 (it's hidden by default in WinXP, but it will be in "List All Modes" under "Advanced") and plug 'er in. Progressive looks so much better than interlace. If you are one of those people who insists of emulating everything pixel accurate, you can use driver hacks e.g. Soft15k and such to get CGA/EGA timings, too (which that monitor will also do and autorange to).
Depending on how it's currently configured, you may have to move the video cable going from the input board with the VGA connector to the other plug. That controls signal levels. It comes set from the factory for PC signal levels, but it may have been moved if it was used with the higher arcade signal levels. If things are really dim, you probably need to do this.