It's hard to find laptop that doesn't have built-in Wi-Fi these days. As a matter of fact, if you buy a new and relatively high-end model, such as the Dell XPS M1330 (which I have and really like), chances are your laptop even has built-in 802.11n card.
Even though the new N specification (officially called Draft N 2.0) is not yet ratified as a standard, more people are taking advantage of this specification for throughput gain. In theory, the N specification can offer speed up to 300Mbps, that's three times of the regular wired connection. In reality, it is just faster than 802.11g standard. Draft N is backward compatible with 802.11g, meaning your existing Wi-Fi equipment should work with the specification, albeit at a slower speed.
However, for the high speed to be achieved, your access point or wireless router has to support the specification. If you are about to setup a new network, it makes sense to buy a Draft N 2.0 router, such as the Trendnet TEW-633GR or the D-Link DIR-655. However, if you already have an 802.11g network, it could be a lot of work (not to mention the extra cost of equipment) to port the existing network settings from the old router to the new one. This is especially true when you have network with a lot of different advanced functions being used, such as port forwarding, VPN, remote access, and so on.
This is the situation where I would recommend the Trendnet TEW-637AP Easy-N-Upgrader. This is an access point that is easy to setup and manage. You just have to hook it to your existing router, turn it on, and run the installation wizard on the included CD. In a few minutes, your wireless network will be upgraded to the Draft N 2.0 specification.
I tested the TEW-637AP anecdotally and it offered basically the same throughput and range as the Trendnet TEW-633GR router. The best thing about the TEW-637AP is that it's very small, about 40 percent the size and weight of Draft N 2.0 access points from other vendors. For about $60, I think it's worth it.