I had 7.5" wheels on the front and rear of my car. Both were 32 offset, and I had some gap in the rear that looked fugly IMO. Offset is just how far off the mounting hub is placed from the centerline of the wheel. So the larger the number, the futher away the hub will sit, and the wheel will be brought into the wheel well more, creating that gap everyone wants to get rid of. For a 7.5" wide wheel, mojo is right, you would want an offset that is down in the 30's or lower. here are some pics of my 7.5" wide 32 offset front, and 8.5" 37offset rear wheels. You can see i have a little room to play with.
http://www.tirerack.com/wheels...d=101thats a good page explaining offset. The only thing they don't mention is that most of the wheels you will find today are not going to be negative offset. All are positive offset readings. Even then, an offset in the low 10's to 20's can still give you that deep dish look, if you're going for that.