what is the optimal resolution for the monitor? (you can use the menu and buttons on the monitor to find out) don't forget refresh rate!!
Also, this may be a longshot, but I had a program on my computer called shades(it lets you dim the display separately), i found if shades was running when I plugged in the other monitor in. if you have some third party screen/color app. turn it off unplug the monitor and plug it back in (do it while the comp is on) calibrate the display BEFORE your turn your programs back on.
one last thing... is that apple displays have pretty dense pixel counts compared to other monitors(especially one from 2004 Im myself have an 05 lcd display and it is really blurry compared to my mac screen) You might just be used to seeing osx on a high pixelf-per-inch monitor.
My monitor is really blurry so I primarily use it for movie watching(or things that don't require lots of reading) it's a 17" 1280x1024@75Hz so you'd think it would look decent. but next to another apple display theres no contest