As well as the frameset option suggested by robertc, you could also make the page refresh most or parts of itself via a HTTP request made by client-side javascript.
This would mean that the page would never be left with an error displaying (or blank, while the browser waits for a timeout to occur if the page is inaccessible) and if the machine is slow this can reduced on-screen flicker during page updates (you can record the last result and not update anything if the information hasn't changed), though it would be a little more work to implement than the simpler frameset option.
Of course if you want an error page to be displayed (instead of the "last known good" information which may at that point be out-of-date) you can display your own message styled to match the theme of the usual display, or perhaps just add a warning to the usual display to the effect that the information shown has not been updated for a while.