My mate has used them before and thought they were shite on keeping speed continuos etc, although that was about 3 years ago so maybe they've improved somewhat. Not sure what you mean by your last question? But I'llhave a guess. You want to look for the the 'gHZ' that the product sends the signal at. For example I'm on Virgin Medias 10MB connection, and using wireless I get about 8.5MB, so I lose about 1.5, although its no noticeable on downloading, browsing etc. The router that I showed you sends the signal at 2.4ghz.
If you get what I showed you, its simply a matter of opening your PC up, slotting the wireless card in (It will only go in one place, and comes with clear instructions), closing your pc back up. Connecting your modem to the router with an ethernet connection (the connection that you currently connect your modem to your pooter), then thats it mate. Turn your computer on, and install the software and it will automatically search for wireless networks thats in reach. Look for the strongest on (yours) and click connect...done.
If you need any more help mate, just ask.