"I keep losing my network connection to the server, or to other computers in the workgroup. Internet access is generally OK. The problem seems to crop-up as s oon as I stop using the computer for a few minutes, if I keep working continuously on a network document, then everything is OK, but as soon as I stop...."
Recent LAN chips/cards (wired, and in some cases wireless) have an option to "turn off this devce to save power." - In principle this seems like a laudable, planet-saving idea, but in fact the tiny amount of power saved would only concern a laptop-user on batteries - and even then, maybe not.
Issue here is that the powersave option makes the computer disappear from view on the LAN, and quite rightly the server assumes that the client has packed-up and gone home for the night. Thus it closes the file-sharing session. When the user next tries to access networked files, there is a delay whilst the connection to the server is re-negotiated. Some programs treat this delay as a fault, and report it so.
Go to Control Panel, and open the Networks item.
(under Vista/7 there's an additional step of opening "Change Adaptor Settings")
Highlight the affected connection, right-click it, and and select "Properties." You should see a pane something like this:
Press the Configure button next to the card/controller itself, near the top.
You'll see a multi-tabbed pane something like this. Look for a "power" or "advanced" tab, usually the rightmost.
Here the powersave option is active, so this card likely WILL give trouble if used to access a fileserver. Untick the option.
Unless you have a pressing reason to require "Wake on LAN" then leave the other option unticked, too. Otherwise your computer may develop a habit of suddenly and unexpectedly springing to life.
Interestingly the dialog warns lengthily of the possible side-effects of Wake On LAN, but completely omits to mention the problems that powersave can cause. Which in most cases are far more of a concern.
OK your way out, and the problem should be cured for this card. Repeat for any other network connections. (other than dialup)
There is generally no need to reboot, you should see the effect straightaway.
As an update, recently had a situation where one of our own notebooks was regularly losing the wireless connection. It transpired that the powersave setting on the wired LAN adapter had mysteriously turned itself on, and that this was adversely affecting both network adapters. Took a while to spot this one, I must add. So, where such problems exist, remember to check the settings for all adapters. Even one with an empty socket can be the culprit that's causing your connection to drop.
For an unrelated problem which sometimes gives rise comparable symptoms - involving 'Disconnected' network shares - see this Microsoft Technet page. In this case the fix (a registry value change) needs to be applied to the computer hosting the share. The page mentions NT/2000 but the advice applies to all recent Windows versions.