Using Safari 3.1 and WebKit nightly builds on WindowsXP. r3446 works fine but r31727, r31733, and r31786 will not open and give "safari cannot open a browser window and may be missing important resources" Sorry I can't pin down better revision but these are the windows builds available.
This bug should be marked as a duplicate of bug 18376. It has been fixed in r31819, but there is no Windows nightly available yet after r31786.
*** This bug has been marked as a duplicate of 18376 ***