If you are already realtiming to a laptop, then the cable you're using should work.
If you haven't got that set up yet, there are a couple of things you'll have to watch out for.
Since you're in this group, I'll have to guess that you have a Stentura 8000. If you are thinking of using digitalCAT as your CAT software of choice, then you absolutely CAN NOT use a Keyspan adapter -- which is what Stenograph will sell you if you ask for an adapter.
BUT, if you're not using digitalCAT, then that Keyspan adapter will work well.
One thing I like about that particular adapter is if you have multiple USB ports, it will work in all of them. It's been a while since I used mine, but I think you don't have to adjust the COM port settings in your CAT software.