So is it legal to start websites with these domain names. They will

not be associated with google or youtube or Orkut. They may provide some services which may be in parallel with youtube or orkut. OR they may provide services which are not related to orkut or youtube.

SO my basic question is : IS it legal to develop such kind of

websites? (if one already owns the domain). (DO ask me if u need any clarification for the question)

I've yet to know of any law saying you can or can't register this or that domain name. But there ARE certain laws limiting their usage, especially trademark laws.

However, some domain names can cut too closely to unique and famous trademarks (e.g. xerox, nissan, etc.) you'll have a hard time showing you have no intent whatsoever of infringing their trademark rights, especially if you don't intend to put up any hint of commercial use whatsoever. No adsense, no parking ads, nada.

The links below can give you more info on what uses are limited. Note that the 1st one, ACPA, covers only the US and its territories, so other countries might have their own similar laws.

Your usage of the domain name can also be restricted by your provider's legal fine prints (more often than not called a "service agreement"). It essentially tells you what both you and the other provider can and can't do.