Tables \"flyver\"?

Hvorfor ligger mine tables ikke præcist op ad hinanden i IE5.5 - de gør i Netscape 6 !

<TABLE BORDER=\"1\" CELLPADDING=\"0\" CELLSPACING=\"0\" ALIGN=\"CENTER\">

<TR><TD WIDTH=\"285\" HEIGHT=\"125\">
<IMG SRC=\"gfx/bgtopleft.jpg\">
</TD>
<TD WIDTH=\"463\" HEIGHT=\"125\">
<IMG SRC=\"gfx/bgtopright.jpg\">
</TD></TR>

<TR><TD WIDTH=\"285\" HEIGHT=\"237\">
<IMG SRC=\"gfx/bgleft.jpg\">
</TD>
<TD WIDTH=\"463\" HEIGHT=\"237\">
<IFRAME FRAMEBORDER=0 WIDTH=\"463\" HEIGHT=\"237\" SCROLLING=\"AUTO\" SRC=\"iframe.htm\">Din browser understøtter ikke IFRAMES!</IFRAME>
</TD></TR>

<TR><TD WIDTH=\"285\" HEIGHT=\"48\">
<IMG SRC=\"gfx/bgbottom.jpg\">
</TD><TD WIDTH=\"463\" HEIGHT=\"48\">
<IMG SRC=\"gfx/bgbottomright.jpg\">
</TD></TR>

</TABLE>