Club Lexus or Club NA-T would be good places to start. The IS platform has ssen this done numerous times. There have been several feature cars in Turbo magazine and others with this done. Larry at Innovations in Orlando has done this to several IS's. If you are planning on doing a full 2JZ-GTE 6 speed swap get ready to spend about $15 to $20K on parts, etc for everything. If you want to Turbo the GE engine and swap in the 6 speed I would say it would cost about $12K to do it RIGHT. There are lots or people that say it can be done for less but you will spend more in the long run redoing shit that a few extra bucks in the begining would have avoided.
Good luck with your project.