Ummm, no it isn't. It's equivalent to two 17" 1280 x 1024 monitors side by side.
A 4:3 17" monitor is 13.5 x 10.5 and a 29" ultra widescreen (like the dell U2913) is 27" x 10.5". So your 29" monitor is two small 17" 4:3's without the bezel. In order to have 2 - 23" 4:3's your ultra wide screen would have to be something like a 40" ultrawide screen monitor.
Furthermore, 1280 x 1024 on a 23" monitor would look like crud. It'd have a worse DPI than a 27" 1080P monitor!
Related to this, it's surprising how big a 23" widescreen display actually is (or at least it was for me coming from an old 20" iMac). It has WAY more horizontal space than I expected.