Are you talking about around the perimeter of the window, or in weight pockets?... I have to say, this does not sound like a very professional company that you are dealing with.
I'm going to guess that you are referring to the weight pockets. They sell packages of loose-fill fiberglass that work well for that.

The windows themselves are insulated. This was just something extra that I had asked for (since we just had new attic insulation put in I have insulation on the brain...). I asked the window company if they do any insulating when putting in the replacement windows and they told me what I quoted above. But the windows (OKNA 400D) themselves are definitely insulated (Optional foam-filled insulated extrusions add energy efficiency - Deluxe version only.), so I the extra insulation would appear to be for the perimeter. I'll double-check though!

the perimeter of a replacement window always gets insulated; we use low expanding foam. if the gap is too tight, we just caulk the gap. either way we insulate.
i imagine you are talking about weight pockets?

Hmm. I left them a message and am waiting to hear back.

My question to them was "I wanted to confirm that the installers do a good job of sealing around the windows once installed (and do they do anything more than just caulking, such as any sort of insulation?)"

Their response was "For the insulation process, the windows are already insulated. If you would like extra installation you will have to buy it and have the men install it."

I've attached a photo of what I found on the website, not sure if that's weight pockets or not (I'm guessing not).

Aside from weight pockets, is there anything else I should specifically ask the company (i.e. the low expanding foam that was mentioned above)?

Thanks again!

The foam enhanced window insulates , well, the window, certainly not around it.
Ask this. What do they do about the space between the new window and original frame?
Are you getting this info from just a salesman or the actual installer?

I'm told by the salesman that the window will be foam wrapped. He said the foam wrap goes into the cavity of the frame when they remove the existing window, then the window goes into the foam wrap. He said this creates an air tight seal.

im am taking a shot in the dark and giving the salesman a pass. i would venture to guess that the installers know what they are doing.

I hope so as well :)

These guys have really good reviews on Angie's List and other sites so I should be ok...

The foam collar does nothing to stop air so make sure they spray foam or otherwise seal the connection.