wheel width for 03 si?

I'm looking for some rims and I've found a few different ones that I like, but I'm not exactly sure what the wheel width is supposed to be. On discounttiredirect it says for a 17" wheel it would be 17x7, but I saw some wheels that are 17x7.5 and I'm just wondering if I can use them with my car or not. Thanks for any help.

7.5w is standard, if you go past that you have a chance of rubbing..
but there is always a chance of rubbing if your car is lowered

Ok thanks. I guess I was just a little confused because the tires that come with the 17x7.5 rims are the same width as the ones that come with the 17x7 rims which are 205/40/17. If the rim is wider I guess I don't understand how they fit the same tires.

I know that one of the most important parts of selecting wheels is the offset as well, but I dont' know why. I'm pretty sure it has to do with how far the wheels stick out, so it's not just the width of the wheel but the offset also. Anyone want to elaborate?