wireless networking - Can you upgrade a laptop from an 802.11b/g to an "a" or other 5GHz compatible WLAN card?

And if so, is it worth it? All of my other devices run much faster and have stronger signals and are connected on the 5GHz channel (they are also obviously newer so...). I have replaced hard-drives in laptops before and am somewhat familiar with getting in there, but would love some feedback. Thanks in advance!