I use a Canon 1Ds camera and i am a first time user of PM. I download some images that I just shot and when i enlarge them by double clicking they are pixalated and soft looking What's use here
The Canon 1Ds by default only includes a very small embedded preview in its RAW files. There is a custom function you can enable that will embed a much larger preview if you want.
If you're on Mac OS X 10.4.3 and higher (you didn't mention what OS you're running) then you can enable RAW rendering in the RAW tab of the Preferences dialog. Then set the For RAW only: popup menu to Render RAW for Preview if possible. You will then see very high resolution previews.
HTH,
-Kirk