Copies of Ubuntu can be obtained by downloading the disc images directly from the internet ubuntu.com, Internet mirrors and via Bit Torrents.
The optimal amount of memoery for a netbook running ubuntu is a 700 MHz processor, but depending on the verison that you wish to install makes a differeacne
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Yes absolutely one can install Ubuntu or any other OS without internet connection. Of course you have to have the Ubuntu .iso image file handy. You can install it using USB stick with universal USB installer or from the hard disk you have downloaded to. But the latest updates won't be installed without internet.
You will need to make a bootable USB stick. The Ubuntu LiveCD should include a tool to do this.
Ubuntu is binary-compatible with it, so you could technically install and run it. However, a system that old might have problems running Ubuntu well, especially if it doesn't have enough RAM.
It should be as simple as plugging the ethernet cable from the modem into the computer. Ubuntu is generally smart enough to figure out how to configure the connection.
Ubuntu is safe. The majority of viruses and other malware on the internet are written for windows, so they wouldn't affect an Ubuntu computer. However, ubuntu is less user friendly than windows, so I would be careful and make sure you have a good backup for your windows computer.
You will have less disk space available for OSes.
There's no native build for it. But you can get it running on ubuntu using WINE which i don't recommend. But the default chat client that comes with Ubuntu is way more better(Empathy). It supports multiple protocols as well as audio+video streaming(webcam), filesharing etc.
Do you mean, install Ubuntu and not enter the BIOS? To install Ubuntu using a CD, you need to enter the BIOS, setting the CD drive as the first boot. Otherwise, the computer will still boot off the hard-drive and ignore Ubuntu on the CD drive. If you meant, install Ubuntu without removing your Windows operating system? Then you need to set up a dual-boot between Windows and Ubuntu. Search the internet for fuller instructions on creating a dual-boot. If you simply want to try using Ubuntu without making any changes to the OS already on the hard-drive, either use the CD containing Ubuntu as an ISO file, known as a Live CD. Or, look up WUBI on the internet. Wubi will allow you to download and use Ubuntu as you would any other Windows file - without making any changes to the hard-drive.
Xubuntu and Ubuntu are two different versions of Ubuntu. (Ubuntu has GNOME.)