jaroslav.tavgen,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
#one:hover+#two,#two:hover {
display: block;
}
#two{
display: none;
}
</style>
</head>
<body>
<span id="one">Pervaya Stroka</span>
<span id="two">VtorayaStroka</span>
</body>
</html>