Some people have been experiencing an ongoing issue where the Finder in Snow Leopard will crash either when navigating through folders or when scrolling. As is described in this Apple discussion thread, in some cases the problem seems to be random, but in others it appears to happen more regularly.
Unfortunately there is no apparent fix for this issue, but people have at least found temporary success by running general maintenance routines and fixes on the system to revert settings and customizations back to default. Here are some that you can try:
Remove the Finder preferences
Go to the /username/Libarary/Preferences/ folder and remove the file "com.apple.Finder.plist" and then log out and log back in. If you cannot scroll through the preferences folder because of the crashes, then enter the following command in the Terminal to accomplish the same task:
In addition to removing the preferences, try going to the Finder preference settings (in the Finder menu) and view options (in the View menu) and disable features in there. In particular, disable the options to calculate all file sizes, and showing icon previews. Keep in mind that you will need to set these settings for all folder views (grid, list, column, and cover flow). Additionally, if you set these settings for one folder (i.e., your home directory or "Macintosh HD"), you can then click "Use as Defaults" to apply them to all folders.
Remove DS_Store files
It is possible that corruption in individual folder settings files could be contributing to these problems. The Finder uses a hierarchical system for inheriting settings in new Finder windows, so while it will by default use most settings from the first opened window, it will still interact with each .DS_Store file it encounters. Corruption in these files could cause the Finder to quit and relaunch.
To remove these files, try using a utility like BlueHarvest to clear them from local drives (especially the boot drive). You can also use this utility to prevent the .DS_Store files from being created on non-mac disks and mounted network folders. Keep in mind that doing this will remove custom folder views, and also prevent them from being set, but may help you troubleshoot the problem.
Run full system maintenance with OnyX or other utility when in Safe Mode
Download "OnyX" or another cleaning and maintenance utility (Cocktail, Snow Leopard Cache Cleaner, Yasu, TinkerTool System, and IceClean), and then reboot into Safe Mode before running the utility to perform maintenance tasks. Doing this will ensure minimal system resource usage during the maintenance routine which may result in a more thorough cleaning.
Be sure to run permissions fixes (can be done with Disk Utility as well), and remove the boot, kernel, preferences, directory services, font, and other system and user caches. In addition, you can use these utilities to rebuild the launch services, but should also be able to do that by running the following command in the Terminal (copy and paste if needed, since it is fairly long):
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -seed -rfv -all user, system, local
Keep in mind that doing this will revert custom file associations, so you may have to set up the "open with" options for files again. Lastly, be sure to run the built-in daily, weekly, and monthly maintenance scripts.
This problem could be related to the Finder error -10810 that we covered in a, so try some of the suggestions we mentioned there, including reapplying the latest OS X combo updater (the latest one being for OS X 10.6.2, though 10.6.3 is just around the corner). As a last resort, you can try reinstalling OS X, which will perform an "archive and install" by default, preserving your user data and settings. As such, doing this should not change much in your system, but you may have to reinstall some applications.