PowerShell doesn't have support for Symbolic/Hard Links currently. There are improvements on this front coming in PowerShell 5.0. The latest preview (September 2014) includes some of this functionality. You may want to peruse the release notes (docx):
To support symbolic links, *-Item and a few related cmdlets have been extended. Now you can create symbolic links in a single, simple line with New-Item.
An example:
New-Item -ItemType HardLink -Path C:\Temp -Name MyHardLinkFile.txt -Value $pshome\profile.ps1
There isn't an example for Copy-Item, but I assume it would be simple to use this with a recursive Get-ChildItem and pipe the results to New-Item, but you would have to try it yourself.
In the meantime, the PowerShell Community Extensions project has a New-Hardlink cmdlet. From the looks of it, you would have to do as I described above and pipe the results of Get-ChildItem into this cmdlet to create a hardlink for each file.
