Here's what Sword of Truth Wiki has to say about sorcerers:
"A sorcerer was a magic-user that could not be harmed directly by a wizard's magic. Their Magic and a wizard's magic were different - like oil and water. Likewise, a sorcerer could not directly harm a wizard with his magic." -Click here to go to the sorcerer's page
Here is what it says on wizards:
"A wizard was a man that could use magic and was the male counterpart to a witch." -Click here to go the wizard's page
-I'll give you a bit of my own opinion on what the difference is.
Using an old idiom, the difference between sorcerors and wizards is the difference between apples and oranges. They are both fruits, they both have seeds, they produce juice, and in general are pretty tasty, too. However, they are fundamentally different, even if they are the same in many ways. The apple is hard, the orange is soft; the apple's peel is hard to remove, while the orange's is easy to pick off with fingernails; the apple has a hard, bitter core, while the whole of the orange is edible, even the peel.
While they don't repel each other like the opposing forces of a wizard and a sorceror, they certainly aren't the same.
A wizard trying to use his magic on a sorceror is like trying to get an orange tree to grow apples, or vice versa: it just doesn't work, and it's pretty pointless to try. You can get around it in circuitous ways; for example, you could tie a bunch of apples held up with string to an orange tree. The tree still didn't grow the apples, but it kind of looks like it did. It's the same way when a wizard tries to use his magic on a sorceror--he can harm him indirectly, by knocking a block of stone onto him, perhaps, or throwing up dust to blind him with a wind created by magic, but he can't turn the sorceror into a dog or cast lightning at him.
All in all, the difference between them is simply that they're different. They are similar, but fundamentally opposed in dynamics.
Further, this brings up some questions from me as well. A sorceress is the female counterpart of a wizard, this is presented to us as fact. There are also sorcerors, which I can infer is the male version of a sorceress. A sorceress is usually a great deal weaker with her gift than a wizard, but still formiddable in her own right, and their magic is similar enough to a wizard's magic that they can, with enough time, teach a wizard to use his gift.
So, if a sorceror is the male version of a sorceress, and their magic is fundamentally opposed to the nature of a wizard's magic, and a sorceress's magic is similar to a wizard's, I can only conclude that there is a female counterpart to a sorceror, which would be the female version of a wizard. The logical conclusion, to me, for this is confusing: the female version of a wizard might be a witch. Or, in the context of the Sword of Truth series, a witch woman.
This has some disturbing implications, firstly that a witch woman would thus be immune to a wizard's gift, which would explain why even wizards were afraid of Shota, and conversely that witch women couldn't use their magic to directly affect a wizard. I've looked very carefully at how Shota and Six have used their powers on wizards in the past. With Richard, Shota has used illusory spells on occasion, which I suppose might just veil her physical form, and not actually affect Richard's mind. She did, however, pin him to the wall of the Mud People's spirit house with her magic, so she might either be beyond a sorceror's limitations, or just have used a trick to get around them.
Six also used circuitous methods to circumvent a wizard's power: she created a counterspell that only turned the magic back on its user by effectively allowing the magic to fall on its face, and didn't actually shield against it. She also went out of her way to use Princess Violet's talent with art magic to capture Richard's gift, by whioh we can ascertain that she was not able to do so on her own.
We also know that a witch woman's ability to view the flow of time can be interrupted by the presence of a wizard's magic, which would lend at least some credence to this theory.
Second, a witch woman is feared by all, mostly because of her ability to ride the eddies in the flow of time, but wizards would know better than most that such an ability is not a reason to fear someone. One of the few things that seems to frighten wizards who are in control of their magic is either something that renders that helpless, or something that is more powerful than them. If a sorceror, the male version of a sorceress, who is weaker with her gift than a wizard, is on equal footing with a wizard, and a witch woman is the female equivilant of a wizard, and wizards fear witch women, that would imply that a witch woman is stronger than a sorceror, and thus stronger than a wizard.
All conjecture, but it's fun to play what if.