I am in the USMC and I just got married a few weeks back and been doing paper work like a mad man. We just turned the I-130 into the Tokyo Embassy on May 07 2008. Now we were thinking what was next. I leave to go back to the states on the 23rd of May. Any info would help.

if all the papers are OK (did the consul check?), your part is done. Next, the consulate will contact your wife with the instructions for medical, and to collect other papers and schedule the interview.

My tax return wasnt with my I 864 but they told me just to give it to her when she comes back in with the other papers. What other papers are there? About how long is the interview?

For DCF, it'll really only be DS230 Parts I and II (biographic information) for your wife, as well as a medical check and police reports (for every place she's lived in for more than 6 months from the age of 16).

It's impossible to say how long the interview will be, or even what questions she'll be asked. It varies greatly between consulates, consular officers and the couple's situation.