There are som stronger PS experts here than me but I'd say defintiely not by your description. If you go into the menus and select "image size", you will have a number of boxes come up in a window that will tell you the overall size of the image, the pixel and inches size of the image and towards the bottom, the resolution of the image. In this resolution box, you will hopefully see a resolution of 300, not 72 unless you either shoot with a low megapixel camera or have resized it previously. If you have an image whose resolution is only 72, then find the original size or .....
1. upsize the image in no more than 10% steps (this will give you a better result than going straight from 72 to 300 but it's not great)
2. buy one of the commercially available resizing programs that have specific algorithms for upsizing images and making them look good.
Hope that helps...
"The girlshapedlovedrug messes with my mind." Gomez (the band)