Sanchita,
The myarchicad site should give you a temporary student license. I don't know if that student license key works with the full download... but imagine it should, as Artlantis uses internet activation.
The download there is provided as a service/convenience to students ... but as Mark says, it is not a Graphisoft product.
I don't know that Mark's link will give the proper release downloads. The official download page is here:
http://www.artlantis.com/en/downloads/
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