Little bit more than that.
The TZ5 and 4 share the same lens, body and menu system, but not the same sensor. The TZ4 has a 9MP 4:3 format sensor capable also of standard def video in 16:9 and 4:3 formats. The TZ4 also has 16:9 capabilities for shooting pictures, but it's not native to the sensor. Instead the TZ4 crops the tops and bottoms of the picture to get to 16:9
The TZ5 has a multi-aspect sensor capable of true 4:3, 3:2 and 16:9 shots, including all 3 at the same time. Additionally, that sensor can do 720p video at 30fps. The other BIG advantage of the TZ5 vs. TZ4 is it has a GORGEOUS 430K pixel LCD screen vs. the TZ4's 260K pixel LCD. The TZ5 will be easier to see in bright light, and playback on the TZ5 is wonderful.
Image quality is about the same, but (in short) the TZ5 gives you more native picture modes, HD video mode and a better LCD. It's worth the money for most folks, but if you are on a tight budget, the TZ4 is also a nice camera.
check out
http://www.dpreview.com to compare the two directly.