first i was thinking to buy some ubuntu based netbook like asus 1225c but its not 64 bit however i hada look at macbook air which is expensive but in light weight category it has i5 processor as well as 4GB DDR3 Ram

other than that of anyone has opinion regarding a 64bit ubuntu netbook please share ? how good it is to go with macbook air ?

Remember if you buy one with a good proccessor you can always upgrade the Hard drive, ram, fans. If you find a windows notebook with good spec you can always install ubuntu onto it. If you were to go with apple the macbook pro has very positive reviews but unless you specifically want an OS X operating system you can get more for your money with windows netbooks, but you still want the speed right? The ASUS Zenbook Prime UX31A has speed, very positive reviews and an i7 proccessor all for the price of the macbook air.

is it available in India ? or does it have backlit keyboard and how much it weigs ?

It does have a backlit keyboard, it weighs 1.3 kg and you will have to find out if it's avalible in india.

however this is a good factor of macbook air Up to 5 hours wireless web

Up to 30 days standby time

Built-in, 35-watt-hour, lithium-polymer battery

i guess i can also install MAC OS on Asus Zenbook,

No, no you cant. However you may be able to install ubunto on MAC but im not sure, you would have to look into it. What will you be using the netbook for?

programming and testing code in diff platform, develop tools for maya (3d animation software) and Foundry Nuke (VFX compositing package)

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