I've used Coreldraw for years as well and have found it invaluable for this type of work. I have pulled off some good decals (black toner only) at 1200 dpi from raster images, but most will benefit from the smoothing of vector art. As Peteski points out, many logos are available online either at sites like his url (great site, by the way!) or from the company itself. For instance, when making some CN decals, the company helpfully has the logos for download in different forms.
For those of you stuck in the pre-digital train era, scanning documents might be more effective than working with images from rolling stock, etc. There are also some excellent font matching sites to help you get the right lettering if you need it. I've had some success using this site
http://www.myfonts.com/WhatTheFont/ with cropped images of the text I want that I have obtained from pictures and other sources. It is not always perfect, but might be helpful.