... I make sure not to touch the Windows partition (NTFS).
When dualbooting w/ Linux you need to create a SWAP partition and a bootable ext3 or ext4 partition mounted to "/"
Now, I haven't used Wubi 'nor EASUS, so I can't help you with those.
As long as you don't touch your NTFS partition it will stay in tact. If you install Linux over it, well, it's gone.
Ubuntu uses GRUB and I choose to install GRUB on the Master Boot Record.. But when you do that and decide to delete Linux, you won't be able to boot into Windows and you'll have to fix the MBR with boot discs (from what I know). So be careful with that.
I am a using a ubuntu installation I downloaded to a cd. When I get to the partition wizard I get confused about the slider. In the 27.1 g ( a partition I created with EASUS ) free space it allots 24.6 to/dev/sda3 and 2.5 g to ubuntu 9.04. Now I can change this with the slider but I have no idea what the ideal setting will be. I also uninstalled Wubi Ubuntu but the choice still appears when I boot. Is that going to be a problem? Is there a danger that the installation will wipe out Windows? Thank you for any help. Dan