about virtual box
 

I've downloaded virtualbox. Do I've to install it in my home folder or can I install it other window drive like 'D' or 'F' drive and run other OS inside it?

http://www.virtualbox.org/manual/ch02.html#id2648299 indicates that on a Windows machine you download the executable and then double click it.

rich_c: AFAIK the OP wants to install VirtualBox in Linux.

jone_kim: Bbefore downloading VirtualBox from the website, see if you can install it from your package manager (Synaptic or Ubuntu Software Center if you want a GUI).

You can install it either in your home folder, or any other place you like, just need to check out the website to see what commands you need to install it to your preferred location. Either way you will need root prividges to do it, and need development libraries install. Vbox will need to build modules for the kernel for it to work

I am running Ubuntu 10.04 in my machine and want to install virtuual box.
Can I install windows XP in virtual box and will I be able to run C #, ASP.NET from that?

I have run xp under vbox in slackware, but have not installed C# .net software,so I couldn't say if they will install or run correctly.

Definitely you can install c# and .net software if you have given virtual XP about 1 GB of RAM ...

How can I allocate dyamic RAM to virtual box???????

You can't. It would be akin to removing and plugging in RAM modules in a real PC, which wouldn't end well...