Guano, I had that same crap happen, too. Only thing that eventually fixed it was going back to IE4.0 (after a reformat - I hope for your sake THAT part isn’t neccessary), and then going straight to 5.5.
Just wanted to second the opinion that 5.5 was much buggier, unstable, and slower on my machine (Pent. 550 Mhz, 128 mgs ram). I went back to using 5, no problems.