For this project you will need -
-Arduino Ethernet Shield
-PIR Motion Sensor
-LM35 Analog Temperature Sensor
As far as software goes, the Arduino IDE should be the only one you should use. Now, to build a webpage to serve up, you will need to have a basic to intermediate knowledge of HTML. If there is one place I know to gain a good understanding of HTML (and Java, consequently) it's http://www.pageresource.com
. That was and is my go to resource for making webpages. I was introduced to that page back in high school, and have referred to it since. A vast wealth of information there!
If you already have a good understanding of HTML and Java, you can move on :)