Hi,
My guess would be,
Go to skin1/customers/main/products_t.tpl
Find the code...
Code:
{math equation="floor(100/x)" x=$config.Appearance.products_per_row assign="width"}
And replace with this
Code:
{if $product.categoryid == 248}
{math equation="floor(100/x)" x=3 assign="width"}
{else}
{math equation="floor(100/x)" x=$config.Appearance.products_per_row assign="width"}
{/if}
Let me know if could solve your problem?