If you're not familiar with identifying your networks settings:
Start > Run > Cmd > ipconfig or ipconfig/all
As far as wireless extenders, they work, but they are no different than when it comes to determining the location of your wireless PC's. If you are attempting to connect devices in the furthest part of your house, the extender should be placed in a location, say halfway between or further, where it receives the strongest signal from the router. Placing it near the router defeats the purpose as the signal the router and the extender sends are nearly identical and redundant. I use Linksys myself, no extender, because the people I know who use the extender say it's useless and most moved to the Dlink Extreme-G. I will be doing the same.
Another complication is the use of 2.4ghz wireless phones in the house. If you have them, you may want to consider changing to 5.8.