Nautilus is the file manager like windows explorer in Ubuntu - it comes up as 'places'.

I don't use Xubuntu as much so I can't remember the equivalent, but it's on the menu (right-click on the desktop if you can't see this?) and is similarly easy to use.

It probably won't call the partition the D: drive, but it will probably be in the list as 'file system', and should 'mount' (let you go into it) when you browse to it.

If you're not planning to dual-boot, when you install you will be nicely allowed to repartition the hard drive and it will give you the default option to pick if you're confused...

Hope that helps!

thank you. so what i will do is that i will put my data in a portable HDD and then delete all the XP partitions and make new for Linux while installing Ubuntu

by the way, i might try Mandriva first as my PC is 2.4GHz, 512MB RAM and 80GB HDD

I think Ultimate Edition is the best Ubuntu based Linux Distro. Just have a look: I have tried all distros but ultimatly sat on ultimate edition.

http://forumubuntusoftware.info/viewforum.php?f=69

Linux Mint and Ubuntu are easy to use for software management. Personally I have been using Linux Mint 9 since it's release.