I have the same CPU as you, Biglad, and mine is currently running at 44°C. Obviously yours is a little higher, but I don't think it's reaching a critical level just yet. However, the 'chirping' sound could be either your heatsink fan, or your case fan starting to show signs of wear, and if either, particularly your heatsink fan, are not running efficiently, that may explain why your CPU is slightly on the warm side.
That's just a suggestion - sorry, can't help with the rest, but just a question - when you were having trouble booting into XP, did Win98 start OK?