I would toss a coin.

These two cameras are clearly aimed at the same buyer.

Here is a link to a side-by-side look at their specifications:

http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=konicaminolta_dimagez5%2Cpanasonic_dmcfz5&show=all

As you can see from the specifications, while the cameras are quite similar, they do have differences.
When you look at those differences, you have to decide if they are "must have" or "doesn't matter".

Image quality and detail is important.
You can see sample photos at these links:

http://www.steves-digicams.com/2005_reviews/fz5_samples.html

http://www.steves-digicams.com/2005_reviews/z5_samples.html

As you can see, they both take excellent photos.

To my eye, the detail for the FZ5 photos is a bit better than the Z5. But see what your eye says.

Before you decide you should go to a camera store such as Circuit City, where you can get your hands of each camera.
That is where most people make their final decision.
They usually take an instant like or dislike to the look and feel of a camera at this point.

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