# this does not support all the features of runas.exe, but is a first stab
Function Start-UserProcess {
    param([Parameter(Mandatory=$true)][string]$Username, [switch]$SaveCredentials, [Parameter(Mandatory=$true)][string]$Program, [string[]]$ArgumentList)

	  $pArgs = & { $Program; if ($ArgumentList) { $ArgumentList } };
    $strArgs = ($pArgs | foreach { "\`"$_\`"" }) -join " "
    $saveCred = if ($SaveCredentials) { "/savecred" } else { "" }
    runas.exe "/user:$Username" $saveCred $strArgs
}

# examples:
# Start-UserProcess -Username "MyDomain\MyUsername" -SaveCredentials -Program "notepad" -ArgumentList "C:\Temp\myfile.txt"