6th gen SE wheels and 350Z wheels? What's the difference?
 

Is there a difference? My guess is that they're the same style but the Z has wider wheels?

If u look at the spokes, they're different. Also, the Z wheels are 18x8 30mm offset. The 6th gen Max wheels are 18x7.5...not sure of offset, but I'd guess more like 40...

Also, aren't the Z's staggered??? I thought the fronts were 18x7.5", 33 mm offset and the rears 18x8", 30 mm offset (I may have the offsets reversed).

Z's are staggered for sure. Also as CCS2k1Max points out the offset is different. Stock offset on a 6th gen is 40mm. Going down to a 30 is quite a change.

they are all same size but come w/ different size tires

We're all correct. Depending on the model/option, the Z's 18"s can be staggered, wheel and/or tire size. The coupe can have 18x8.5" 33 mm rears. This is from the 04 Z owners manual (I left out the 17s):

Size Offset
in (mm)

Coupe Aluminum
Front
18 x 8JJ* 1.18 (30)
Rear
18 x 8JJ* 1.18 (30)
18 x 8-1/2JJ* 1.30 (33)

Roadster Aluminum
Front
18 x 8JJ* 1.18 (30)
Rear
18 x 8JJ* 1.18 (30)

The 18x8.5 is probably referring to the Track model rims by Ray's. The Touring/Performance models came with 18x8 all around. Just 225 tires in front and 245 tires in rear. I have a set as well. Don't believe me? Check 350Zmotoring.com