Its all relative -- if you have hardware renderred particles on a GeForce emitting 10,000+ particles per second, with multiple emitters, and 32x multisampling you're going to get issues.

Regardless -- there are a few things you can do. If you particles are not software (should be either Cloud, Blobby, or Tubes -- and have a (S/W) beside it) and you're running a GeForce... you either need to switch to a software-compatible emitter, take the lack of stability/quality/speed -- or softmod to a Quadro. (Or radeon to a FireGL)

Turn down the multisampling or use a more optimized format. That's all videocard drivers most likely... unless its software -- in which case you may need to get more RAM (or just wait)

Cut down on the realtime previews... do the minimal necessary to see your dynamics at a certain frame -- then testrender... clear... and do again if necessary. Better yet -- playblast and come back when Windows Media Player comes on.

You get the idea -- do whats necessary -- go overboard if you don't mind waiting... cut back if you need to do it quicker.