I am untreatable fan of Softice
. It is possible to run Softice under Vista also (it's better - after little exports modification in Vista kernel files), although it has only basic functionality and is not as stable as under systems it was designated for. But you can easy Ctrl-D at any time to view the ring0 code and you can trace through the code. The processes list, changing contextes - don't work
So it's necessary to make old simple tricks as inserting INT3 in the start of the debugged file - to get into proper context to set breakpoints in debugged process. All it is reasonable only if you are interested in ring0 code tracing. For ring3 tracing you have a lot of other debuggers as listed above