Actually, what you should do is figure how many inches you're planning to print your render at, then multiply that by 300. Like, if you're planning to do 8x10 inch prints, then you'll have to render at 2400x3000 pixels. 720x486 @ 300dpi is only going to give you a 2.4x1.62 inch print. But changing dpi is pretty easy; just bring your saved render into Photoshop, go to Image > Image Size and deselect resample image, then in the box that's labeled Resolution, erase 72 and replace it with 300 then press OK. I'm sure there's something pretty similar in Paint Shop Pro.
Hope this helps and I hope this clears up any confusion.