Disable Opening Finder Window

I'm sure this isn't the kind of solution you were looking for, but i believe the answer to your question is "no".. However, if you download X-Assist (http://members.ozemail.com.au/~pli/x-assist/) , and use the "old style" application switcher (the one in the upper right hand corner a la OS 9) when switching to the finder, no new window!

I also tried switching via drag thing's switcher, but it opened a new window.

In addition, if you use 'command-tab' and 'command-tab-shift' to switch to the finder, no new window, but that's a bit tedious...