Here's a follow-up for anyone interested in the above configuration. I bought an Apple minidisplayport to DVI adapter at Bestbuy, and had no success with the Viewsonic. I was going to try VGA by attaching a DVI to VGA dongle to the Apple DVI adapter, but no joy there. The dongle requires DVI-I and the Apple adapter only has pin sockets for DVI-D.
I exchanged the DVI adapter for a minidisplayport to VGA one. Success! The MBP immediately found and recognized the Viewsonic by model number, and even installed the correct color profile. The monitor's resolution is 1680x1050 which is the same as on my MBP's 15" hi res antiglare screen. Also, this monitor's screen is just as sharp on VGA as it is on DVI.
The bottom line is that, if you're having difficulty getting an MBP to connect to an external monitor by DVI, try VGA. It will most likely work.