I'm on my second Thinkpad, an X31 which is a strong performer except for an exceptionally long boot time. The only real problem that I have experienced showed symptoms similar to those that Gaucho100K was getting and I eventually managed to figure out that it might have been due to firewall incompatibility. It appears that first TPF and then ZoneAlarm seemed to be clashing with the Microsoft firewall in the system, causing a great deal of instability and hangng.
I was reluctant to abandon the system firewall, but was ready to do so until a friend recommended another freebie called Outpost. I don't yet know how good Outpost is since I only installed it yesterday, but right now it is working smooth as glass with the rest of the system, and if it continues this way, they can even have a few dollars for their "advanced" model whenever they come calling.