i am not sure where to put this thread. i thought this would be the appropriate place.
i have a Dell Inspiron laptop with 250 GB hard disk. i have two partitions C: and D:.
the C drive has around 60 GB and D: has around 190 GB. i am using windows vista and want to add Ubuntu as well. where should i install Ubuntu ? would installing in D affect the other files that i have in this D partition.
Do i need to format all and create other partitions so as to install Ubuntu.
i have installed most of the softwares in the program files in D drive. so if i install Ubuntu in D drive, will it work properly without my initial data being lost ?

I'll be glad to get reply.

First off. Where is your Windows Vista installed. Second. Ubuntu will only need about 20 gigs total to run fine. Third. You could try a Wubi install of ubuntu inside of Windows Vista till get your feet wet using linux. Sounds like you have stuff scattered all over the place. Any formatting on any drive will erase any data on that drive. Let me know what is exactly set up on your partitions so I can guide you a little better.

Do i need to format all and create other partitions so as to install Ubuntu.

Actually that is the way to go. Till i know exactly where your Vista is on which drive, I can guide you from there.

i have vista installed in C drive .
and almost all of the softwares i use are installed in D drive

my main question of concern is : can i install ubuntu on my d drive without formatting anything. if i do so would it cause any problems or whether my any files will be lost ?

n i don't want to install ubuntu inside windows . i want them to work as two independent OS

my main question of concern is : can i install ubuntu on my d drive without formatting anything.

No You can't. You will have to format . Which will wipe data on D. Your files will be lost.

n i don't want to install ubuntu inside windows . i want them to work as two independent OS

I think you misunderstand how WUBI works. Ubuntu will be a seperate operating system. The only difference is the install procedure and where Ubuntu will be located. At your Windows Vista bootup screen you will be given the option to boot up either Vista or Ubuntu. When Ubuntu is running, Vista is Dormant. You will not be able to bring Vista online as a operating system while you are running Ubuntu till you reboot.

I suggest if you wish to install Ubuntu on it's own partition that you install it on C Drive instead of D drive. Here is a link for Dul booting ubuntu with Vista with screenshots.
How to dual-boot Vista with Linux (Vista installed first) -- the step-by-step guide with screenshots

This tutorial shows Installing Ubuntus Latest Release 9.04.