A small amount of code, registered the current directory of all the DLL to the GAC, please copy the gacutil.exe into the same directory.
$Path = Get-Location
$Dir = Get-ChildItem "$Path" -Recurse
$Dlls = $Dir | Where { $_.extension -eq ".dll" }
$Dlls | ForEach-Object { .\gacutil.exe -i $_.name }