Yeah, the opening starfield is an interesting change.

The starfield was changed along with the crawl in 1981. There's also a change in the moon (either a moon went missing in 1981, or one was added, I don't remember which).

Then, in 1997, the starfield (and moon) was changed back to its 1977 version, but the crawl remained in its 1981 form.

I don't know what the deal is in the 2004 version, but the STAR WARS logo certainly recedes far too quickly in that one. I think it retains the 1977/1997 starfield, but I could be wrong.

I also know that the starfield in the second shot is different in the 2004 version, but I don't know if that change is present in the 1997 version or not.