1. First, run a scandisk or checkdisk. Let Windows fix any errors.
2. Run a disk cleanup utility...this will flush your temporary internet folder, trash can, temp system files, etc.
3. Delete any garbage files or data...if possible, run a Duplicate File Finder program.
4. Run Defrag on all partitions (NOTE: run this after you have deleted all trash and excess files!)
5. Run a registry cleaner utility and delete or get rid of any orphaned entries in that registry.
6. Check your exisiting swap file for it's size and location (*will explain location later in the post). If you have alot of ram (i.e. 1 gig and over) set this swap file to something small, like 250 mb. The reason is that this will force Windows to load more into memory, resulting in faster performance (note: some games and applications actually require a certain sized swap file so check your applications performance after making a size adjustment for any error messages.)
