Qué tal,
prueba así
<p align="center">
<form action="xxx" method=post
style="display:inline">
<input type="submit" name="Submit" value="Si" >
</form>
<form action="xxx" method=post
style="display:inline">
<span lang="es"> &nbs p; </span>
<input name="Submit2" type="submit" value="No">
</form>
</p>