W3C XHTML Transitional Validation Problems

Couple questions I have regarding W3C XHTML Transitional Validation.
How can I solve some of the following probelms:
no attribute "background" for <td width="50%" background="/images/bg.gif">
no attribute "height" table
there is no attribute "onChange".<select name="nav" onChange="go()" class="formboxes">
reference to entity "T" for which no system identifier could be generated....shared.com/news/news_item.aspx?ID=6&T=News Story", 454, 390)'>
I am unsure how to solve these problems, could someone help me please?use css, for example:
<td style="width:50%; background-image:url(Images/bg.gif)">

and
<table style="height:100px">

Dont know why it's bugging you about the onchange event... maybe because of the capital C?

Fredrik K wrote:

use css, for example:
Dont know why it's bugging you about the onchange event... maybe because of the capital C?

Yeah XML is case sensitive and XHTML attributes and tags are all defined as lower case.

Thanks very much for your help. The only other problem I need to sort is:
reference to entity "T" for which no system identifier could be generated. ...shared.com/news/news_item.aspx?ID=6&T=News Story", 454, 390)'>

Also when I attempt to validate a stylesheet for CSS2 standard it fails because i have not specifed a background color. If i then do the following background-color : transparent; I get the error You have no background-color with your color. I dont want to actually specify a colour, anyway around this?

One other problem I am getting is the following
ErrorLine 577 column 179:there is no attribute "language".

...') Page_ClientValidate(); " language="javascript" id="txtSend" class="formbut

This is not code I have wriiten, it is rendered when the page is displayed. Is there anyway of fixing such?
Any ideas anyone?

Niall,

ASP.NET 1.x does not generate XHTML compatible code. For example, it outputs script tags using language='javascript' instead of type='text/javascript'. You simply cannot modify the internals of ASP.NET 1.x to change this.

The solution is to switch to ASP.NET 2.0 which generates XHTML compatible code.

Thanks very much for your help.
Anyone have any ideas about my other problem's?