One Box to Rule Them All ;]

Ok, so i had such problem than Snow Leopard Dock and Finder crashes at boot time (login time). Mac boots, logging in, and that's it - basically you cant do nothing else because Finder don't work, sometimes Dock not working also and sometimes even that bar on top not working (however its called).

After many hours of trying to fix that solution for me was:

If at least Spotlight is working (upper right corner)
Launch terminal, go to home ~ (aka home directory) and check if there is no shortcuts (alias, links) to not mounted disks (for example USB sticks, virtual disks, dmg). If you found such links - delete them. I guess you will have to do same with ~/Desktop/ ~/Downloads/ ~/Documents/ (for me it was only ~). After do "sudo reboot".

If even Spotlight not working
Reboot Mac (holding power button) and hold Cmd+s while it will start booting. You should boot in single user mode. Then you have to mount disk / (don't remember exactly how but you will find instructions on screen "mount /aaa/bbb /". Tipe "bash", "cd /User/<your user>/" and do same deleting actions as described above. After "reboot"

I don't know if you having same problem as i did, but i guess its worth trying :)