vBulletin has an internal RSS system that you can use to add RSS feeds to your forum.

To manage your RSS feeds, log in to your vBulletin admin area and go to RSS Feeds > RSS Feed Manager.

To add a new RSS feed, click the [Add New RSS Feed] button.

Every existing RSS feed listed in the RSS Feed Manager can be edited by clicking either on its name or on the [Edit] link next to it.