The difference is generally size, weight, and battery life. Netbooks typically are smaller, lighter and generally get better battery life. Netbooks also dont have cd/dvdrom drives built in. Linux is a complete different OS from windows and you wont be able to use windows software on it (easily). There are however many free "clones" of many windows applications, and yes you can get on the internet with it. Sounds like you've never used Linux before, so i'd recommend playing around with a friends computer that runs linux to see if its what you want before buying something just because its cheaper.
Cheers.