I stuck with Microsoft products above so that you could see how products in the same line you're using today can satisfy your needs, but of course many other vendors offer similar home wireless products at the same (or better) prices. As long as you stick with products intended for home use (e.g., Linksys, D-Link, Netgear) you should be able to install and configure wireless devices like these yourself. Although not necessary, choosing a wireless router and adapter from one product family may reduce setup problems, and you might even save money by purchasing a router+card bundle.

Note that I have not yet addressed your use of Vonage. You don't say whether you're using a Cisco or Motorola TA with your VoIP service or how that's connected to your existing network, so I'll guess that your TA is connected by Ethernet to the same base station as your PCs. You'll be able to connect that TA to an Ethernet switch port on your wireless router and accomplish the same thing.