I didn't use J.Doe's answer, but I assume that it's correct because it's similar to what I ended up doing. When linking the original XML schema:

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <xsd:element name="Root">
        <xsd:complexType>
            <xsd:sequence>
                <!--Below are the primary vehicle descriptors - essentially the attributes for the cars-->
                <xsd:element name="Brand" type="xsd:string"/>
                <xsd:element name="Model" type="xsd:string"/>
                <xsd:element name="Colour" type="xsd:string"/>
                <xsd:element name="Price" type="xsd:string"/>   
            </xsd:sequence>
        </xsd:complexType>
    </xsd:element>
</xsd:schema>

Excel assumed that there was only one record in the sheet. The solution to this was to create a second complex element (in addition to the element named "Root") in my schema, which contains >1 of my Root elements. The resultant file looked like this:

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <xsd:element name="Car_Table">
        <xsd:complexType>
            <xsd:sequence>
                <xsd:element ref="Root" minOccurs="0" maxOccurs="unbounded"/>
            </xsd:sequence>
        </xsd:complexType>  
    </xsd:element>
    <xsd:element name="Root">
        <xsd:complexType>
            <xsd:sequence>
                <!--Below are the primary vehicle descriptors - essentially the attributes for the cars-->
                <xsd:element name="Brand" type="xsd:string"/>
                <xsd:element name="Model" type="xsd:string"/>
                <xsd:element name="Colour" type="xsd:string"/>
                <xsd:element name="Price" type="xsd:string"/>   
            </xsd:sequence>
        </xsd:complexType>
    </xsd:element>
</xsd:schema>

When adding the schema using Developer > Source > XML Maps > Add, you get a prompt like this:

Select the element which references the other element (as this allows for recursion). In the XML source panel, the map will look like this:

You can then map each element in the schema (Brand, Model, Colour, Price) to the corresponding column in the sheet. Once the schema is mapped to the sheet, your data will look like this:

You can then export the data to XML by going to Developer > Export. After Selecting a filename and directory using the export dialog, the resultant XML file should look something like this:

This was done using Excel 2010, other versions will differ somewhat.