I have been using ubuntu and kubuntu for past 3 years. I know the general layout difference between various DE (i.e GUI level). but I am interested to know the basic technical difference between various DE, that is the difference in file mgmt, memory mgmt and so on. could anyone suggest me a good site or e-book where i can get all the information regarding DEs.
No. I've been playing w/ different linuxes for years and the major DEs have always been Gnome and KDE & the smaller Xfce, although there are other simpler, smaller DEs. I doubt there is a significant difference in the way they treat hardware and I imagine the software mgmt will vary from Desktop to Desktop.
These days, w/ all the live CDs available, I suggest you try out a bunch and see what you like best. As I understand it, the DE choice has always been a matter taste.
I prefer Gnome, but there are millions who swear by KDE, and others who want a less memory intensive DE like Xfce.
You might try this question at linuxquestions.org, since you'll find somebody from just about anywhere and whatever taste there.