CrossRoads:
Virtualwire does not use the UARTs - its more like smart software serial.
Data rate should not be higher than 2000 and messages sent under 27 bytes (or 37? check virtualwire document) due to time needed for message encoding/checking.
I agree. Keep it down to 2000 bps and limit the chunks of data you're sending to a few bytes to begin with. 27 bytes is the maximum length.
I'm using similar models running at 434MHz all the time and they've never caused me any problems at that speed.
As CrossRoads said earlier, encoding and error checking and everything is done within the library so garbled data will never show up on the receiving end.
You will only see data that has passed CRC check
I'd say that you don't need to add an antenna at all if you just want to test them at short range.
For longer ranges you should get a wire of a more precise length and not "just a wire". You could use quarter, half or even full wavelength if space permits.
What version of VirtualWire are you using?
I'm using version the latest version which is 1.9 with Arduino 1.0. Get it at http://www.open.com.au/mikem/arduino