Can I Delete This File?

Let's start with first things first. If you're getting that kind of message, then as a novice user you may be poking around in places that you're better off leaving alone. For example, if you're clicking around in your folders, find a large file on your hard drive and decide to delete it to regain a bit of disk space, you may well be deleting an important part of the operating system. The warning message you mentioned in your question is there to make sure you don't shoot yourself in the virtual foot.

A good rule of thumb for inexperienced users is this:

Don't delete ANYTHING unless it's a file you know you created. If you do word processing, work with spreadsheets, graphics, email, etc. then open the program that created the files, and use it to find and delete the file. In most cases, you can use File -> Open to locate the file, right click on it, then select Delete.

If you are familiar with Windows Explorer, you can use it to navigate to the folder that contains your files and delete them from there. But again, only delete files that you recognize as ones you created.

If you no longer need a software package that has been installed on your computer, DO NOT try to remove it by finding and deleting the folder where it resides. You'll probably end up deleting only a portion of it, and Windows will complain about missing files next time you start up. Instead, go to Start -> Control Panel -> Add/Remove Programs, and remove the software package there.

If you're concerned about your hard drive filling up, take these steps: