The one from Best Buy is a Router/WAP, since you already have a router, it is not neccessary that you have this.
The other one is a WAP only, this is what you need. I don't know anything about this brand so I will not comment on it.
I myself have a Netgear wireless router/WAP and I am very happy with it. I would suggest that you buy the same brand WAP as your router (makes it easier for support but it is not neccessary).
I would also suggest
www.pricegrabber.com for your purchase, might be cheaper than COMPUSA $$$.