Windows 98se limits

I need a refresher on the limits of win98se will run on. My in-laws just got a P4 3.2ghz machine with 512Meg. I remember that 9X doesn’t like more than 511Meg. I also remember hearing the it doesn’t like PCs over a certain speed, but I can’t remember what that was.

So my questions are:

1 – What happens with more than 511Meg?
2 – What was the fastest machine that 98 can handle? And what happens beyond that.

Thanks in advance.

Tim