I don't know that I'd rush out and buy more memory. The ammount of RAM will affect performance but what you are saying is that it won't even run. I only have 392MB in my system and before that 256MB. Poser 4 runs fine with either configuration. 512MB should be more than enough for Poser 4 and for sure Poser 3 to run normally. OS is more important. 98/98SE is going to be flakier than XP/2000 but that in itself shouldn't keep Poser from running. I think it's more likely to be a conflict with either a driver or a background application or a setting. I seem to recall someone a few weeks ago posted something similar about the input error message and an LCD monitor (perhaps it was you?). I'd try to set up a boot configuration that's as bare bones as possible to eliminate possible conflicts and try that. Did you have broadband before? I don't know if that's a possibility as well.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken