Go to versiontracker and download the following:
Onyx - for cleaning, repairing permissions etc
Printer setup repair - to get rid of all the printer drivers you'll never use
Whatsize - for checking out all those massive files that you never knew you had
Delocalizer - to get rid of all the laguages you don't need.
These last three will help you free up a load of hard drive space, which, as dllavaneras suggested, will help. Be a bit careful with Whatsize - only delete files and applications which you know about and understand, and if there's anything you don't recognise, either leave it or find out what it is.
Most important of all, use something like CarbonCopyCloner to back up your drive before you start, just in case.....