I had two way contact via the ISS repeater last August. See video.
International Space Station repeater contact between VK6YSF and VK6FG. UHF down-link was with a 70cm Skew Planner Plan antenna and a UHF mast-head pre-amp. VHF up-link was 100 Watts and a 2m Ground Plan antenna.
All you want to know about the ISS and more can be found at these links. The second link is a GPS track of the ISS and other satellites! I find both of these very helpful! Contact the ISS and AMSAT - Satellite Tracking