This had been rumored for a while, but HBO made it official today: "In Treatment" will be back for a second season, with at least Gabriel Byrne and Dianne Wiest reprising their roles. Playwright turned "Criminal Intent" producer Warren Leight will take over from Rodrigo Garcia as showrunner -- as I understand it, Garcia's not leaving the show; it's just too difficult for one man to be in charge of that many episodes -- and the show will be relocating production to New York, no doubt for Leight. (Paul's practice will still be in a Washington, DC suburb; my guess is either he'll be in a new house or we won't see much of the exterior anymore.)
In terms of other returning regulars, the press release simply says "Additional cast members will be announced as they are confirmed." In the Israeli original, a few of the first season patients continued into season two, notably the Jake and Amy counterparts.