Is it possible to display which runways and taxiways are which in the online radar screen?
no, just use top down
Runways are simple to workout, also get an airport chart for the specific airport you need.
Runways are designated by their headings.
Runway - 09L & 09R would be 90
27L & 27R would be 270
If you want to see the aircraft on taxiways and runways, download FSM Moving Map. It is a neat little program that shows mutliplayer and your aircraft on Airport Charts or Sectional Charts.
Download it from here:
The program works well, but if you find a problem about it not working after a certain date, you might need to set your computers date back to the date the program was last worked on; this was a bug and I don't know if the guy from Ranainside fixed it yet.