Not too sure - I'm not an expert but have setup some Wanadoo (now Orange) kit for friends and family so know the ins and outs of them... and what a pain they can be!
As for the channels, that's not quite right. There are different specifications (read: speeds) of wireless which your computer may be able to work at.
The spec is IEEE 802.11 x, where x is a letter and the most common in use are:
802.11b - operates at 2.4GHz and supports upto 11Mbps, ~ 100 feet range.
802.11a - operates at 5GHz, upto 54Mbps, ~ 100 feet range.
802.11g - operates at 2.4GHz, upto 108Mbps, ~ 100 feet range.
I think these are the "channels" that you have been told about. The problem with the 2.4GHz range (b and g) is that this is the UK's "anything goes" range, so it gets flooded by everything from microwave ovens to bluetooth to video senders, so sometimes you can get interference on them.
The channels you can "see" in your wireless networks section are just other people's home/office networks. Unless you have the keys for them, you won't be able to get into them, and as such it shouldn't interfere with your network. The range is quite poor on wireless, especially as brick walls soak up the radio waves quite nicely, and this is why wireless is quite an attractive, low range option.
So, in summary, there's not much you can do about selecting "another channel" unless your hardware supports it, and you'll probably be running b or g anyway, and because they operate at the same frequency it won't make any difference!
As long as you're not actually connection to the other networks, it won't slow down your connection, but it may (slightly) degrade the quality of your connection.
So don't worry about it
