I use Powershell, remember to run as administrator
$getDLL = Get-ChildItem ".\YOURDLLFOLDER" | where{ $_.Extension -like "*.dll" }
[Reflection.Assembly]::LoadWithPartialName("System.EnterpriseServices")
[System.EnterpriseServices.Internal.Publish]$publish = new-object System.EnterpriseServices.Internal.Publish
foreach ($dll in $getDLL)
{
$publish.GacInstall($dll.FullName)
}