Caffeine!
Deep breathing and ample caffeine?
What IM program do you use? I use Adium (Mac OS X), which not only logs my conversations for future reference but also allows me to keep multiple conversations open in tabs instead of separate windows. I keep Growl (Mac OS X) open and it pops up a little bubble for each new conversation piece so I can quickly see if something needs responding to or not.
I also LOVE Spaces (also for Mac OS X), which allows you to switch between multiple screens. This makes toggling between programs a LOT easier.
This may sound trite, but really mastering keyboard shortcuts has made my life a lot easier, no matter how crazy the client's office is that I'm in. Since I've gotten to the point where I use most every shortcut available without thinking about it, I can navigate between windows and perform a number of tasks in a lot less time with a lot less stress.
Marina