Well there are alot of things you could try. You could look on the internet for tutorials, or you could go to your local book store and buy a few books that specialize in that category.
If your still a highschool student you should take a class in computers and even if your not you can still take a class at a local community college. Taking classes at community colleges are pretty cheap, it might be around 50 bucks.
Also there is a program out there called video professor, it focuses on teaching alot of microsoft programs, specifically ones you've already mentioned. At this site http://ipods.clickperks.com/?r=376139, u can try a free trial, just fill out the form as if u want an ipod, and just try the free trial instead.
Where can i go to learn how to work with computer programs such as microsoft excel, outlook and powerpoint?internet explorer 6
Many colleges have free software training. There are also a lot of books like those "Microsoft excel for dummies" books thats should be helpful. Also ask your friends who are currently administrative assistants to explain the basics to you. Good Luck!