Again, the DPI number won't have any real effect on the image... a "300 dpi" image that's 1024x768 has the exact same resolution and total pixel count as an identical image that's "75 dpi." The only difference (in Photoshop) is in printing size and the image size percentage that shows up in the image titlebar (an image set to "75 dpi" may show the size as 100% when viewed on screen while the same image would say 25% if set to "300 dpi".) Just set the dpi correctly if/when you print or translate to another format and you'll be just fine.