I read that Russians were selling them the new SA-300 system. Are they the same thing or is there a difference?
The S300 uses the SA-10 (or SA-N-6 (Navy variant)) missile. The system (S300) allows for tracking of 100 contacts and targeting of 12/24/36 contacts. Latest versions of the SA-10 missile can travel at Mach 6 and engage targets at Mach 8.5.
...So a very capable missile with a method of engaging multiple targets. It can self target in the terminal semi-active homing phase so the target will not know of the threat until just prior to missile impact.