Vertical center of webpage, vertical center

Vertical center of webpage, vertical center
<! DOCTYPE html PUBLIC "-// W3C // dtd xhtml 1.0 Transitional // EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> Vertical center of webpage

Only tables are used!

<Table border = "0" width = "100%" id = "table1" cellspacing = "0" cellpadding = "0" height = "100%">
<Tr>
<Td valign = "middle">
<P align = "center">
</td>
</Tr>
</Table>

Q: How can I center the page vertically?

Which man can give me some advice, I am grateful, and the webpage is ready. The customer asked me to let the page vertically center the browser to view the original post>