You can adjust the priority of any process through the task manager (CTRL-ALT-DEL).
Right click on the process in the list on the Processes tab, then select Set Priority. The options are from real time to low. You may want to experiment with the settings. Giving one application real time may starve everything else, so doing something like lowering a heavy duty application slightly and raising skype slightly might work out better.
If you find a settings that works better you can also set the priority in a shortcut. So as an example the notepad shortcut is,
"C:\notepad.exe"
And would become,
"C:\WINDOWS\system32\cmd.e
xe /c START /high C:\windows\notepad.exe"
To run as high priority.
This does not change priority for network traffic - just for the executing of the process. So if you are using Skype but also running torrent applications or video streaming it probably will not help. If your applications are just local it likely will.
There are 3rd party applications that can be used to control the bandwidth available for your different applications. Netlimiter is an example,
http://www.netlimiter.com/The free version would allow you to see what is going on, the shareware version actually lets you set limits. I don't know of any totally free programs for this offhand.
