Jaxel has created an attachment slider module that lets you choose the size of the image, how many you want in a row, how many you want to show total. For instance, 8 in a row, 30 total on the slider. And it lets you choose which forums you want the slider to pull from. It lets you choose whether you want it to put it on the home page, forum index, in a forum or in a thread. It's awesome and has been included in the latest version of Xenporta. Check it out.
http://xenforo.com/community/resources/8wayrun-com-xenporta-portal.90/