In Data\Sites\1\skins\artisteer31-hovermenu\style.css, you can replace all instances of 1000px with your width of choice (e.g. 1200px). That may or may not work perfectly, since a lot of the widths in skins are interrelated. Once you make the change, go to Administration, Advanced Tools, Design Tools, Cache Tool. Click the Reset Skin Version Guid, and that will clear any skin cache you and site visitors have, so you will see the results of your change.

Ultimately, the best way to modify the delivered skins is to get a copy of Artisteer and directly load/modify/re-export the .artx file included in the ArtisteerFiles download on Codeplex, by using the Creating Skins from Artisteer HTML Templates document. If you buy Artisteer through the link in my signature or from an ad on this site, a portion of the sale will go to fund the mojoPortal project.

Jamie