Are you living in a neighborhood with lots of WLAN activity ? You can check this if you do search for WLANs on your computer and find lots of them listed. It does not really matter if they use an encryption like WPA, WPA2 or WEP, as long as they are listed there they might interfere with your own WLAN channel which can be the cause for bad download rates and sudden disconnects.
Most WLANs use the same default channel when they ship from factory. This is most of the time channel 11 and sometimes channel 6. Most users keep those default channels which can lead to the mentioned WLAN problems if your neighbors use that same channel.
I would therefor change that default channel if you are experiencing difficulties like disconnects in your WLAN. The default channel needs to be changed in the WLAN router only, the computer will automatically pick the signal up without modification. I’m going to show you how a change would look in my WLAN router.

My U.S. Robotics Wireless MAXg router can be accessed locally with the IP 192.168.2.1. You need to consult the manual of the router to find out how you can access the router interface. The main interface loads after supplying the username and password.
The Wireless tab at the top lets the user change the wireless settings. I had to click on advanced settings to change the default channel from 11 to 3. You should try to raise or reduce the channel by 3-5 steps if possible. This can be an impossible task if you have dozens of WLANs in your neighborhood; My advise would be to start with the low channel numbers and work your way up until you find a channel that works nicely.

Protect your Wireless Lan
How To Change Default Programs In Windows
Change The Default Windows XP Search Engine
Change default and preferred applications in GNOME
Change The Default Web Browser In The System Tray
Change Default Mail Client In Windows XP