I hate to be the bearer of bad news, but I have been told that phpmotion is currently "banned" from use on DreamHost. There are several problems with the script, causing it to be extremely hard on system resources.
Apparently, one of the issues is that the program needlessly forks new php processes in some circumstances where it shouldn't (for example, exec'ing php -v in order to obtain the php version number).
Here is one previous thread from a couple of months ago in this forum that discusses the issue:
There is also a recent review on HostScripts.com that confirms the problem:
I'm not saying that you cannot install it, and if it is only rarely or occasionally used you may have no problem. I just feel you should know that if the program sees any significant usage, you should expect that DH support will contact you about disabling the program, and if it negatively impacts the server and the other users sharing it, they may disable it before contacting you.
According to DreamHost staff I have communicated with regarding this, this is a known problem with phpmotion and DreamHost has attempted to resolve this with the author, but has not been successful.
As a result, DreamHost has been disabling phpmotion when they find it creating a resource usage problem, and that has been what has happened in most instances where it has been installed.