Vista - newb - replacing an old "sweep" program, exec an external program

I am just getting started with PowerShell, again. I am building a
replacement for an old utility that would start at the current directory and
iterate down through the folders and simply execute the command given on the
command line.

Sweep.exe CMDTORUN PARMSFORCMDTORUN

This doesn't work because it seems like it wants to know where the program
is. And if it is an internal cmd.exe command I'd have to know that. I'd
like to just dump what ever the $cmd onto the prompt and let it go. Just
like perl backticks.
I know the attrib could be readily done in the script, but this isn't for me
to use.

So how do I go about executing an external program without knowing its
location or whether or not it is an internal cmd.exe command?

Thanks,
jeff

$cmd = "attrib -a"
$dirList = Get-ChildItem -path $baseDir -recurse | Where
{$_.psIsContainer -eq $true}

foreach ($dir in $dirlist)

{

&$cmd $dir.fullName

}