Not normal, no. Vista is known however to be a bit buggy to put it mildly. And, as Vista is still very new to most folks, it could just be setup improperly. It could be something with Vista or with another device(s) causing intermittent interference with the wireless signal. Also, some ISP's like to shut down on your bandwidth when it appears to them that you are not really using all of it. If this is the problem and happens at inappropriate times, it might be a good idea to run a page like this:
in the background to keep the bandwidth up. Replace the two image locations with ones of your own. The live one must exist and be on a server that allows this type of request. Most do, but - for instance, Google does not. Use one from your own site if you don't have a transfer limit. It can and should be a relatively small image.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<img src="some_local.gif" onload="setTimeout('window.location.reload(true)',10500);">
document.images.src='http://www.somedomain.com/images/some_live.jpg?c=' + new Date().getTime();