When I was bored i just checked to se if the site really was a valid xhtml 1.1 ... it was not! ... a few misses :D
Which section did you test? What error did you find?
I tested mainpage:
Line 31, column 84: there is no attribute "border" (explain...).
...f="http://www.thebestisp.net" border="0">
^
Line 102, column 70: value of attribute "method" cannot be "POST"; must be one of "get", "post" (explain...).
...name="LsLogin" action="/index.php" method="POST">
^
Line 165, column 32: there is no attribute "language" (explain...).
script language="JavaScript"
^
Line 165, column 44: required attribute "type" not specified (explain...).
script language="JavaScript"
EDIT: I tested all the main-sections and it was the same misses on all of them
(I removed "" at javascript cuse it didnt show )
All of them are in the main header...no biggy.
border=0 removes the link border around the image.
post just needs to be put to lower case, no biggy.
dunno where you got the last line...will have to look at the source when I get home from work in a few hours.