hi can any body help me please..i have installed magento on live server and now i want to import all products and category of a website which is allready running live.. how can
The out of the box tool does not import Categories. There are a lot of modules on MagentoConnect that also import categories. You can also try unirgy.com uRapidFlow.
See the Magento Wiki:
Magento is rather special, so you might have more luck getting answers at their Forum. Also search through the Magento Knowledgebase.
You can try to use 3rd party service to export products database from one server to another http://importexportbridge.xpscommerce.com/
There required to specify source server address, API username, password and destination server details to transfer database data.
Products, attributes, images data going to be transfered automatically to destination server.
Importing into Magento is not a trivial task. You can use their import/export tool but I find it slow and cumbersome. There's an open source importer called Magmi which works with categories.