If you are sharing to computer then Flash and Windows Media allow you to set the width and height. Several of the QuickTime shares allow you to change width/height if you select the right codec (e.g. H.264). All of these are accessed via the Advanced button on the basic settings screen and then in the Video tab in the Export Settings dialog.
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Welcome to the forum.
Is this the Frame Size of your source footage? If so, there is not way to directly accommodate that, but as Neale point out, with some formats, and the Crop, either in Export/Share, or the Effect applied to the Clips in the Timeline, you can output to that.
PrPro offers a customizable Preset, the Desktop, to accommodate oddly sized footage, but not PrE.