Can a post be removed after it has been posted?
Not usually. They are sometimes removed if there is a good reason like personal information is being disclosed or if there are violations of the terms of service. You would have to contact GW.
If you just joined today why are you worrying about removing posts??
NO! Shatty and all that but NO. Well unless of course you want to suck up to the GW and convince them to give you the power to do so.
OK, my curiosity is aroused? What did you post that you want to take off?