The only way to do this properly is to either pay to have the negatives scanned , or to buy a scanner capable of scanning transparencies, and scanning them yourself.
I suggest buying a scanner, and doing it yourself, as this gives you the most control, and if you plan on scanning a lot of images, will be much more cost effective. I don't know what your budget will allow, but right now the best balance of price to results is the Nikon Coolscan 9000, or whatever they are calling the latest version of that model. It is the closest thing to buying a commercial drum scanner, which costs in the 10s of thousands. The Nikon is about 2,000 and worth every penny.
If your budget is tight then get Nikon's lower end film scanner, over any flatbed, because a flatbed is not designed for scanning negs.
The cd's you get when having film processed are a waste of time, as the images are low resolution, and in the wrong format as well. They usually at best no larger than 4x6 inches at 300ppi or less, which is ok for small prints but useless for enlargements. They are also in jpg format, which is compressed, and not ideal for what you want to do.
I have an older scanner, a HP s20xi, which is not nearly as good as the Nikon's but still better than most others. It allows me to scan slides, and negs at 2400ppi, and outputs in tiff format giving files large enough to work from, though not nearly as good as the 4000ppi the Nikon produces. A typical color neg/slide will produce a file about 25MB in size, as opposed to the 2MB files you get on a cd.
Wolf does somewhat better work in processing than Target, but not that much better in general. I use my local CVS, but only because I know the people in the photo dept well, and trust them to take care when processing film. Most non-professional processing places use the same, or very similar equipment to process film, and give similar results. Wolf tends to be a little better, because they train their employees a bit better, because they are training them to do that one thing, and not as part of overall training like Target.