Hi Brandon,
JPEG is never a good format to create your titles for Premiere. Better use the .psd file or even tiff.
Video uses non-square pixels. Photos from your digital camera use square pixels. So if you start from scratch in photoshop (file-new)you can choose a format with the right pixel/aspect ratio for either 4:3 or 16:9 video. In that case the (NTSC) resolution is 720 x 480 pixels in both cases.
If you have to start your project with square pixels, then you have to correct for the smaller pixels. In that case you start with 720 x 534 pixels for 4:3 video or 864 x 534 pixels for 16:9 widescreen video.
Theo