How can I get a MByte/s or Mbit/s reading of network activity?

Edit: Sorry, I missed the Vista tag.

If you click the Performance tab of the Task Manager and choose Resource Monitor you then get more comprehensive stats including what you are asking for.

But Windows does actually have a much more advanced performance monitor that has been built in for a while and is extremely flexible.

• Choose Start->Run... and type perfmon, then press Enter
• In the Management Console window that appears, make sure that you select Performance Monitor in the left-hand pane
• Click the green + button in the toolbar
• In the Add Counters dialog find the Network Interface section
• Choose <all instances>
• Click the Add >> button
• Click OK
• You will get a graphs with loads of lines on it, thankfully you can delete all the stuff you don't want by shift+clicking the unwanted rows and pressing delete. It's made much more complicated by the fact that you may have virtual network adapters as well as physical ones. You'll have to work out which ones you actually need to monitor.

If you want more details tracing than what the resource monitor give you then you will need to use the Windows Performance Monitor, create a Data Collector Set that monitors performance counters

The performance counters expose a LOT of information about your system that you can record. Here is just what I could fit on screen with the network subsection.

All of those counters can be tracked per interface so you can see which device is using what amounts.

Here is what it looks like when you view the results.

All the data that is records can be exported in to reports like CSV files for any further processing.