What's the difference between Apple TV and Mac Mini?

Can you get Microsoft word for apple Tv? Can you surf the internet? Also, if you can surf the internet by using an iPad for iPhone but use a keyboard and mouse?

MASSIVE difference. Apple TV is a multimedia 'box' where you can watch your programmes on from the internet using Netflix etc. The mac mini is just a computer but compacted into a little and stylish case.
Apple TV = Watch programmes
Mac Mini = Small (and powerful) computer

One is computer and one isn't.

Although the Apple TV and Mac mini look similar, each is targeted toward very different users. The Apple TV is designed to make it easy to present the iTunes content stored on as many as five household computers -- Mac or PC -- on a recent television.
The Mac mini, on the other hand, is substantially more powerful. It is a full-fledged Mac that allows one to do just about anything that can be done on any other entry-level computer -- play DVD movies, listen to music with iTunes, surf the Internet, write documents, create websites, retouch photos, and so forth.
The Apple TV is roughly half the size -- 1.1 inches tall, 7.7 inches wide, and 7.7 inches deep -- of the already minute Mac mini, which is 2.0 inches tall, 6.5 inches wide and 6.5 inches deep.
The Mac mini can be connected to a television -- recent or otherwise -- and do everything the Apple TV can do through Front Row, as well as support higher-resolution H.264 playback and 5.1 channel surround sound. The Mac mini can be configured to receive programming "streamed" from another computer as well. It also plays CDs and DVDs, and with third-party solutions -- and additional cost -- it can be configured to record programming from television.
The Mac mini also can easily support peripherals and external hard drives without hacking. Essentially, far more diverse software and more powerful hardware combine to make the Mac mini substantially more versatile.
The Apple TV also has an HDMI port, component video out, and optical digital audio out ports for easier and higher-quality connections to recent televisions. The Mac mini, on the other hand, only has DVI, Mini-DVI, and/or Mini DisplayPort out and optical digital audio out.
Hope this hopes.