Clean up Micrsoft CRM 3.0 data file

We use Microsoft CRM 3.0 at work. I think it's becoming clogged, and most of the stuff in teh data file is no longer needed. Anyone had experience with removing large amounts of stuff from it?

 

Thanks for that.
I actually want to just remove the old, useless data out of a data file - say 90% of it. Those links at least send me some way up the learning curve - I now know where the data files are likely to be, and I can have a look at them when I get to work. It won't let me do anything remotely.