Croteam has released a demo for Serious Sam: The Second Encounter today. The demo is 110mb and is will allow you to play a portion of the single player game. Download from FilePlanet
You shouldn't, while I am a subscriber I'm fairly sure they have free servers. The only thing with the free servers is that if they're busy your put in line and could wait 20-30 minutes before your download begins. Subscribing basically removes the waiting time.
downloaded this demo a few weeks back, and it is great!....the single co-op level is superb, stick it on 'Serious' and get playing with a few mates, and it's an excellent laugh!
I also D/L'd it too, but I've had some hardware issues that involved reformatting, thus I lost that and Wolfenstien.