OK - AND - the answer is -
The zip.so object has issues in those versions (1.8.0 & 1.8.1) when you directly link it via php.ini - PHP bombs out. My guess is that the XAMPP 'configurators' grokked that out and commented it out in php.ini. Looks like a bad compile.
At this moment - you have two/three options - I can't say what your best one is -
A. use tar.gz compression for .SQL files. (should work)
B. Switch to XAMPP 1.7.7 (was working with zip.so)
C. Build a lamp stack via apt-get/yum etc from repositories.
D. Hang out and see if JonB (or someone else) can get a fresh compile for zip.so working for either of those versions.
E. See if JonB can 'back into' a fix with a 'midnight parts shop' repair...
~ tada ~
in the Old-skool 'AOL voice': "You have answers"