[zmuff]

Wow, nobody answered you. I don't visit this site much, but here goes:

The wheels on an e39 will fit an e34, along with all 5, 6, 7, and 8 series cars (e30 M3 too). You will need hubcentric rings however, to make up for the slight difference in hub size. If you don't, your front end will vibrate.

The bad side is if you own an e39, only e39 wheels fit unless you go aftermarket or have a machinist turn the hubs for you. There's a story of an engineer that lost his job because of this small mistake in hub size, e39's were well into production before it was realized.

There are minor differences in offsets, but not enought to affect clearances. There are big differences in tire sizes though...e38 wheels fit great, but the tires will not fit in the wheel wells right, etc. I have e39 wheels on my e34 with 255/40/17's on the back and 235/45/17's on the front, they fit perfectly.