diypublic

Where would I put this line?
ErrorDocument 404 /index.php?error=404

This is what I see below:

----------------------------------------------------------------
# -FrontPage-
DirectoryIndex index.php index.html index.htm
IndexIgnore .htaccess */.??* *~ *# */HEADER* */README* */_vti*

<Limit GET POST>
order deny,allow
deny from all
allow from all
</Limit>
<Limit PUT DELETE>
order deny,allow
deny from all
</Limit>
AuthName speedingticketfixer.com
AuthUserFile /home/speepcqf/public_html/_vti_pvt/service.pwd
AuthGroupFile /home/speepcqf/public_html/_vti_pvt/service.grp

DirectoryIndex index.php index.html index.htm
#Redirect 301 /index.html http://speedingticketfixer.com/index.php

# BEGIN W3TC Browser Cache
<IfModule mod_deflate.c>
    <IfModule mod_headers.c>
        Header append Vary User-Agent env=!dont-vary
    </IfModule>
        AddOutputFilterByType DEFLATE text/css text/x-component application/x-javascript application/javascript text/javascript text/x-js text/html text/richtext image/svg+xml text/plain text/xsd text/xsl text/xml image/x-icon application/json
    <IfModule mod_mime.c>
        # DEFLATE by extension
        AddOutputFilter DEFLATE js css htm html xml
    </IfModule>
</IfModule>
<FilesMatch "\.(css|htc|js|js2|js3|js4|CSS|HTC|JS|JS2|JS3|JS4)$">
    <IfModule mod_headers.c>
         Header set X-Powered-By "W3 Total Cache/0.9.2.10"
    </IfModule>
</FilesMatch>
<FilesMatch "\.(html|htm|rtf|rtx|svg|svgz|txt|xsd|xsl|xml|HTML|HTM|RTF|RTX|SVG|
SVGZ|TXT|XSD|XSL|XML)$">
    <IfModule mod_headers.c>
         Header set X-Powered-By "W3 Total Cache/0.9.2.10"
    </IfModule>
</FilesMatch>
<FilesMatch "\.(asf|asx|wax|wmv|wmx|avi|bmp|class|divx|doc|docx|eot|exe|gif|
gz|gzip|ico|jpg|jpeg|jpe|json|mdb|mid|midi|mov|qt|mp3|m4a|mp4|m4v
|mpeg|mpg|mpe|mpp|otf|odb|odc|odf|odg|odp|ods|odt|ogg|pdf|png|pot
|pps|
ppt|pptx|ra|ram|svg|svgz|swf|tar|tif|tiff|ttf|ttc|wav|wma|wri|xla|xls|
xlsx|xlt|xlw|zip|ASF|ASX|WAX|WMV|WMX|AVI|BMP|CLASS|DIVX|DOC|DOCX|EOT
|EXE|GIF|GZ|GZIP|ICO|JPG|JPEG|JPE|JSON|MDB|MID|MIDI|MOV|QT|MP3|M4A|MP
4|M4V|MPEG|MPG|MPE|MPP|OTF|ODB|ODC|ODF|ODG|ODP|ODS|ODT|OGG|PDF|PNG|PO
T|PPS|PPT|PPTX|RA|RAM|SVG|SVGZ|SWF|TAR|TIF|TIFF|TTF|TTC|WAV|WMA|WRI|X
LA|XLS|XLSX|XLT|XLW|ZIP)$">
    <IfModule mod_headers.c>
         Header set X-Powered-By "W3 Total Cache/0.9.2.10"
    </IfModule>
</FilesMatch>
# END W3TC Browser Cache
# BEGIN WordPress

# END WordPress
-----------------------------------------

worth a try, will get back to you, thanks