Ive been doin a bit of reading on the russian SAM systems and i dont quite understand the difference between the S-300V and S-300PMU systems, they seem almost identical, fulfiling the same functions, only the manufacturers seem different. can anyone tell me what the difference is?

eerm...difference in range, operational height are the first ones that spring to mind.
The western designations (SA-10:SA-12) also suggest that the SA-12 is more recent (duh ) and thus more capable which infact it very well may be with it's rumoured ballistic missile intercepting capability.

Just off the top of my head...I might be wrong (but I don't think so )