I had a very similar problem. Purchased a Dell Dimension 9200 in May 2007 with Windows Ultimate OS. From Day 1 when recovering from Sleep Mode the ethernet-cable connection to the Dynalink RTA1025W modem/router was always lost. Of course the internet connection at the router itself was never lost, only the Network Adapter connection to the router itself.
Initially this required the computer to be rebooted every time, incredibly annoying for a new system. Various Vista updates seemed to hold hope but none delivered.
Vista could not work out a solution with its own Diagnostics, until one day it (correctly as it turned out) suggested that the Network Adapter needed to be 'reset'. This then became the workaround - enabling the Adapter through the Device Manger Local Area Connection Status for the Network Adapter. Sometimes I would have to "disable" the Adapter so that it could then be "enabled" to get the connection.
The Dell Support site listed the 'latest' driver for the Network Adapter as the file R142352.EXE but this had a 2006 date, well prior to the consumer release of Vista. This driver was also the one recommended by Dell Support as recently as this week.
However, many thanks to sander0501 I found the complete listing for the updated Intel Network Adapter drivers for vista (32 bit) at
Network Connectivity Network Adapter Driver for Microsoft Windows Vista* (32-bit)
The current version of PROVISTA32.EXE is dated 10 July 2007 (or is that 7 October 2007 depending on how you view your dates) and listed as Version 12.2.
In any case I have been using it for several days now and it seems to have solved the Sleep/Network Adapter problem. I will re-post if this does not continue.
It's unfortunate that Dell Support seemed to be so behind the times on this one, I had used the old driver from their support site long ago and of course it didn't fix the problem. Their next recommendation was to be a Clean Install of Vista (arghh-h!).
The PROVISTA32.EXE driver suite has not solved my final major problem with Vista Ultimate. When the auto power option puts (or purports to put) the system into a low power state (which is current listed in the Power Options as Sleep mode), it often does not recover from this, leaving the screen blank and the PC doing nothing. The longer the PC is left after this, the more likely it seems to happen. The only solution is to power-off the PC at the power button and start again (arghh-h!). As you can imagine, the combination of these two problems - Sleep Mode/Network-Adapter and Auto Power Option/Non-recovery - has driven me spare since system purchase five months ago.
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