MIDI on XP is bad indeed, and I have to run my midi application under linux to get a latency lower than human sound perception, without artefacts, and with a cheap soundcard.
I am running PD on several Windows XP machines with a latency of 3 ms (both souncard and pd). I have RME HDSP, Midiman Audiophile 2494 and AC97 souncards on those machines. Even a cheap (intel) mini itx board with a Celeron 1,33 GHz CPU and an AC97 souncard works flawlessly here at 3 ms.
Actually any combination is working. Of course the RME and Midiman cards have a lot lower CPU consumption (around 20%) than the AC97.
I also have MIDI running with no proplem as long as I don't edit the patch. Editing a patch screws up MIDI timing so bad after some time that I have to restart the entire machine in order to get straight timing back.
BTW I'm working at the moment on a very complex sampling engine that requires a lot of juice. So it's not just a simple MIDI in/out patch I'm doing this with.
The conclusion is: if you don't get pd to run on Windows XP there is something wrong with your Windows configuration! Get a clean install and optimize everything for audio performance and it will work.
Ingo Scherzinger