Problem with system hanging

This is so reminiscent of the problems my windoze acquaintances deal with, it's kind of spooky. Every once in a while--and with no rhyme or reason that I can detect--one of my Linux boxes hangs. The only common thread I can find is that I had a Mozilla browser open at the time; I had been using the Mozilla Suite but recently changed to SeaMonkey, and the problem happens with both.

Basically, the way it manifests itself is that my trackball pointer stops responding as it should; the movements are jerky and slow, and then stop altogether; the pointer may disappear from view. The clock freezes; ALL applications open at the time--including terminals--become inaccessible; all keystrokes are ignored. After a looooooooong, painful delay, the Moz browser shuts down; the clock resumes at the current time, and the time lapse from when it froze to when it resumed is usually in the 7-10 minute range.

This is extremely frustrating and I'd like to narrow down what the heck is causing it. I'm using Ubuntu and here's my browser info:

Mozilla-5.0 (X11; U; Linux i686; en-US; rv:1.8.0.6) Gecko-20060730 SeaMonkey-1.0.4

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