Displaying Posts Category Specific within a Multi-column Loop

I am using this to display my posts in multiple columns and it’s working great: http://wordpress.pastebin.com/09HncmWf

Now what I am wanting to know is how can I make the output of the posts be category specific to the category with an ID of 6?

Here is the code if you don’t want to navigate away…

[code moderated as per forum rules - using the pastebin is perfect]