I concur with dr_st. If you want to keep your dock, you can go for another T61; you can also use a T60, T400, T500, or W500. I think the Z61 will also work with your dock. If you're going to buy a model with switchable graphics(standard on W500, optional on T400 and T500), you must turn the discrete GPU on before you can use the DVI output on the dock.
I'm driving two 1920x1080 monitors via my Advanced Mini-dock, one's a 23" and the other's a 21". They work just fine. One majorly helpful trick I've learned is to adjust the clock and phase settings on the VGA monitor separately to overcome the common 'fuzzy text' problem when using a high-res monitor on a VGA input. The site I list below includes a test pattern and instructions on how to do this:http://www.lagom.nl/lcd-test/clock_phase.php