Nomadd released an updated version of his SLP Spawning script for Arma 2 on the BI forums.
You can use this to spawn units and/or vehicles and have them patrol, defend, attack, hunt the players group and lots more.

Quote Nomadd :
I had some time over the holidays to take a hard look at this set of scripts. I wanted to do more with it and did not like some of the ways it did things. So, I basically reworked it from the ground up.
Hopefully, the changes I have made will make a difference.

Changelog:
• various changes
  
• fixed armor not spawning crew but just regular units
  
• added _boat array in SLP_units_config. You can now spawn boats.