LPN = Licensed Practical Nurse
LVN = Licensed Vocational Nurse
My understanding is that the two are in fact the same thing, but have different names in different parts of the US (no idea what the international thought/equivalent is).
The scope of LVN vs RN is given in detail (for CA at least) at
http://www.rn.ca.gov/pdfs/regulations/npr-b-53.pdf
The big distinction that I understand is that although many of the task or skill activities may be performed by either LVN or RN, the assessment and analysis type of things are not in the scope of the LVN.
Note: this is different from saying LVNs can't make good decisions. I speak only to the scope of practice defined. There are many LVNs I'd rather have caring for me than RNs I have little professional respect for.