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Don’t worry we have solution for this step by step
1->first of all you must back up magento version 1.3 with database
2-> then fresh copy of magento 1.7 download
3->then install magento 1.7 when you get configuration setting then you fill old database connection
4->after installation some issues occur in layout
5->you can search some queries from google if any issue please contact me on my email firstname.lastname@example.org any time i will give response you