If you are looking to add magento reviews form to your product page review tab, here is the step by step instructions for that.

Step:1 open: review.xml, in your “layout” directory.

Find following section:
<block type="review/product_view_list" name="product.reviews" as="reviews" template="review/product/view/list.phtml" after="additional">

Add the following inside this block:
<block type="review/form" name="product.review.form" as="review_form"/>
<block type="review/product_view_list" name="product.info.product_additional_data" as="product_additional_data_review" template="review/product/view/reviews-in-tab.phtml">
<block type="review/form" name="product.review.form" as="review_form"/>
</block>

So your final result should be as...

<catalog_product_view>
        <reference name="product.info">
            <block type="review/product_view_list" name="product.reviews" as="reviews" template="review/product/view/list.phtml" after="additional">
                <action method="addToParentGroup"><group>detailed_info</group></action>
                <action method="setTitle" translate="value"><value>Reviews</value></action>
                <block type="review/form" name="product.review.form" as="review_form"/>
                <block type="review/product_view_list" name="product.info.product_additional_data" as="product_additional_data_review" template="review/product/view/reviews-in-tab.phtml">
                <block type="review/form" name="product.review.form" as="review_form"/>
                </block>
            </block>
        </reference>
    </catalog_product_view>

Now clear your cache and check output.