2
Go to admin, template administration and find xoopspartners_block_site.html. Look for
<{if $partner.image != ""}>
<img src="<{$partner.image}>" width="88" height="31" border="0" alt="<{$partner.url}>" <{$block.fadeImage}> /><br />
<{/if}>
<{$partner.title}>
That is a direct copy from my template. I've got it as 88x31 too. This will not change what you see in partners admin though but that's ok no one sees that but you. It's been a while since I've done that change but I'm pretty sure that's where it is.