<input type="button" value="注册" onClick="window.location.href='register.jsp'">
(在当前页面打开reg.jsp)
<input type="button" value="注册" onclick="javascript:location.href='reg.jsp'">
(在当前页面打开reg.jsp)
<input type="button" value="注册" onclick="window.open('reg.jsp')">
(在新的页面打开reg.jsp)