The common thing in both cases seemed to be that the process svchost.exe was taking a huge amount of processor power, as well as a large amount of memory.
I managed to kill the (apparently) runaway process, but that made me wonder.. what was it doing ? Googling for svchost turned up the following information:
Using the actions and commands described in the knowledgebase article linked above, I could figure out what was running, and which subprocesses / services were hosted by the too-busy svchost process.Svchost.exe is a generic host process name for services that run from
dynamic-link libraries (DLLs).The Svchost.exe file is located in the %SystemRoot%\System32 folder. At startup, Svchost.exe checks the services part of the registry to construct a list of services that it must load. Multiple instances of Svchost.exe can run at the same time. Each Svchost.exe session can contain a grouping of services. Therefore, separate services can run, depending on how and where Svchost.exe is started. This grouping of services permits better control and easier debugging.
From A description of Svchost.exe in Windows XP Pro on the Microsoft site.
And now I know that .. what next ?
More when I find out myself !