This may not have anything to do with Powershell. The command-line install for SQL Server is tricky/buggy to begin with.
Suggestions:
Check the SQL Server setup log on the remote machine See http://msdn.microsoft.com/en-us/lib...43702.aspx for details
Try installing on the remote system interactively from a regular command prompt.
A quick web search for SQLEXPR32.EXE command line returns a few blog posts that indicate issues just running the utility from a normal command-line:
http://blogs.msdn.com/astebner/arch...10435.aspx
http://blogs.msdn.com/astebner/arch...spx#605285
http://www.developersdex.com/sql/me...024&page=2
The last link points to an issue if the current user isn't logged in. Don't know if this is your issue, hopefully the setup log file will contain some type of error message.
I don't know of many people using the command-line install of SQL Server and even fewer using the command-line installation + Powershell. You may want to post your question in a SQL Server forum