you don't have a border, how can you see color changing? try<TABLE border=1 cellspacing=0 cellpadding=0>
<TR><TD ID="a1">xxxxxxxxxxxxx</TD></TR>
</TABLE><A Href="adfasd"
onMouseOver="document.all.a1.style.borderColor='#FF0000'"
onMouseOut="document.all.a1.style.borderColor='#0000FF'">啊啊啊</A>
<TR><TD ID="a1">xxxxxxxxxxxxx</TD></TR>
</TABLE><A Href="adfasd"
onMouseOver="document.all.a1.style.borderColor='#FF0000'"
onMouseOut="document.all.a1.style.borderColor='#0000FF'">啊啊啊</A>
<style>
.blue{border-bottom:1pt solid blue;border-top:1pt solid blue;border-left:1pt solid blue;border-right:1pt solid blue}
.red{border-bottom:1pt solid red;border-top:1pt solid red;border-left:1pt solid red;border-right:1pt solid red}
</style>
<TABLE>
<TR><TD ID="a1" onmouseover="this.className='blue'" onmouseout="this.className='red'" class="red">asfasdfafaf</TD></TR>
</TABLE>
<TR><TD ID="a1">hhh</TD></TR>
</TABLE>
<A Href="adfasd"
onMouseOver="document.all.a1.style.border='1px solid #ff0000'" onMouseOut="document.all.a1.style.border='1px solid #101010'">啊啊啊</A>