Sounds like your looking for a temporary fix until the new piping is done. I would modify my previous answers accordingly. Although galvanized pipe is ancient technology for water pipes, for the time you are talking about, it will be fine. Not to say the old stuff won't suddenly decide it's game time, but the new stuff will be OK. PVC, while not legal, would also work OK for a short time on the cold water, but I'd never use it even for a short time for hot water. The biggest problem for a novice installing galvanized is making everything fit. Unless you can just be close, you could be facing a lot of cutting and threading. If close is good enough, you can of find short lengths of pipe at the store or have them cut and thread to your request. I prefer plumbers pipe dope instead of tape on the threads. I'd go with a 3/4" to 1/2" bell reducer then a 1/2" nipple followed by a union. When it comes time to repipe, I strong advise copper. Although it doesn't seem like that big of a job, looks are deceiving. For that reason if no other I'd would urge you to hire a plumber to do the job. You might get it done, but it could take several days.