See if your BlackBerry.alx file looks similar to this (I don't have the 8320 software installed on this computer):
Code:
<!-- Vodafone filesets -->
<!-- 8300 and 8320: only Green -->
<fileset series="8300" Colour="True" Java="1.0">
<files>
net_rim_theme_120_today_320x240_b.cod
net_rim_theme_120_green_320x240_b.cod
</files>
</fileset>
So three major things - 1) remove the vendorID information if present, 2) remove the radio information if present (likely radio="GPRS-WLAN" or something), 3) be sure to add the new filename between the <files> tag.