[help] upload file script

[eluser]Willy Wijaya[/eluser]
Hello guys..

I need to create a site that main function is for sharing data and its free services.
People can :
1. upload data and get download link + erase link
2. there is a limit for file size uploaded, i.e. 5MB.
3. the file remain on the server for certain time, i.e. a month or a week since it last accessed.
4. the file can be renamed and only post certain types, i.e. .zip, .rar, .tar.gz, .tgz.

I think this is not too hard. but I don't know where to start.
Can someone guide me with CI. Sorry I'm newbie.
I'm familiar with PHP and MySQL, but with CodeIgniter not yet. I just wanna try something new.

Thanks.