We have no experience at this time with WinXP SP3, so cannot say whether SP3 is the cause of the problem. If all else fails go back to SP2.
1) Make sure your H8000 is disconnected from the PC.
2) The drivers on the Web Site will be the most recent.
3) You probably now have multiple drivers partly installed – do what you can to clean them up before continuing.
4) Try unregistering the H8000asio.dll – from the Start Menu choose Run.. and enter the following:
regsvr32 -u C:WINDOWSsystem32H8000asio.dll
followed by [OK]. (this assumes you have Windows in C:WINDOWS).
4) Close all other applications before re-installing.