NVIDIA maintains three different legacy Linux drivers that support their old hardware at different stages with the 173.xx.xx legacy driver being their newest of these proprietary drivers. The two bugs that were fixed up in this updated driver was XvMC not working on systems with AGP graphics cards and a bug causing X.Org Server 1.7 (and newer) to hang when restarted. That's it for the changes beyond adding the X.Org Server 1.8 support, which is the xorg-server found within Fedora 13, openSUSE 11.3, and other newer Linux distribution updates. Ubuntu 10.10 is also currently boasting X.Org Server 1.8, but it (along with other distributions updating this fall) should end up using X.Org Server 1.9 that's due for release in one month.
The NVIDIA 173.xx.xx legacy driver is what supports the older GeForce 5 (FX) graphics cards and some of the older Quadro graphics cards. This driver also supports most of the GeForce 6 through GeForce 9 (and some GeForce 200) graphics cards, but that support for now still can be found within NVIDIA's mainline proprietary driver, which is a better choice. The last time this legacy driver was updated was back in February when adding X.Org Server 1.7 support and compatibility with newer Linux kernels.
The NVIDIA 96.43.18 legacy update supports the GeForce 2, GeForce 4 Ti, GeForce 4 MX, and older Quadro graphics cards. NVIDIA has not introduced X.Org Server 1.8 support here, but this update just carries bug-fixes for the X Server crashing under certain rendering conditions with the Ubuntu 10.04 GDM log-in theme and X.Org Server 1.7 hanging when its restarted.
As of right now NVIDIA hasn't updated their even oldest legacy driver (the 71.xx.xx series), but it's doubtful they will especially with their 96.xx.xx driver not even receiving X.Org Server 1.8 support. For those with NVIDIA graphics cards older than the GeForce 5 series, this basically means it's the end of the line for having proprietary NVIDIA driver support on newer Linux distributions. At least there is the Nouveau Gallium3D driver created by the community that supports this older hardware and for the oldest fixed-function graphics cards there is the classic Mesa Nouveau driver.
Those interested in this updated NVIDIA GeForce 5 Linux driver can find the details and Linux x86/x86_64 download links in this post or here for the other driver.