I've noticed it seems sluggish as well, even after dropping the delay down as low a 10ms where it was dead smooth before the 1.8 server. I have no idea what could be causing the slowdown, but I'll run it through the profiler and see what it says.
The windows 98 freezes seem to be related to the checkMobs function and as it doesn't work properly anyway I'll likely be rewriting the entire function shortly. I have no idea what could be causing the lockup on win98 and not winnt, but I've been runing the client for ~20 minutes with it commented out
It's probably some hidden mob with an invalid ID, I'm going to put checks for valid values into the client on all the data stored in the arrays. It's too easy for invalid data to bomb the client at the moment.