there is no attribute "BACKGROUND"

Does any body know how to fix this.
I am trying to validate these html codes through the markup validation.
I have 5 error messages:

1) Line 114, Column 15: there is no attribute "BACKGROUND" .

<td background="images/nav1bg.gif" onMouseOver="this.className='over'" onMouseOu

2) Line 223, Column 74: there is no attribute "BACKGROUND" .

…cellpadding="0" cellspacing="0" background="images/bgleftnav.gif">

3) Line 225, Column 67: required attribute "ALT" not specified .

…ges/blank_leftheaders.gif" width="172" height="45"></td>

4) Line 254, Column 280: there is no attribute "XML:SPACE" .

…js" type="text/javascript" xml:space="preserve">

5) Line 287, Column 61: required attribute "ALT" not specified .

…img src="images/maincontent.gif" width="584" height="45"></td>

If you can get back to me as soon as possible so I can fix it I would really appreciate it. Thanks

re: there is no attribute "BACKGROUND"

1 and 2 are as stated, there is no such attribute in modern markup. Use CSS.

3 and 5 refer to the "ALTernate" text for an image should images not be available, such as a reader for the blind.

4 means you are probably referring to Microsoft Office stuff which has nothing standard about it. Do not use it.