Has it been working reliably in the past?
Presumably you have "Internet Connection Sharing" set up correcly in the "host' PC, with the IP address automatically set to 192.168.0.1 when "ICS" was enabled? Is the "client" PC set to get its IP address by DHCP from the "host"?
Can you be more specific about the "frequent crashes" as this shouldn't be happening? Also check that the "client" PC's SMTP mail server is correctly entered for the ISP you connect to the internet with.
Part of the probem might relate to the MTU setting. Download and run "CyberTweak" from click here and run that in each PC to optimise the settings. Set the "host" up for an "ADSL Modem" (which I assume you are using and not Cable?) and the "client" for "LAN Connection". This will set the correct MTU and other settings. I would suggest that you create a System Restore point first in case you should have problems after making changes. If your provider is AOL, they use a particularly low MTU setting of 1400, which would be the setting required in the "host" PC.