OK, stupid questions...
1.- Battlefield 1942... A.- it is also an SP/Campaign game. B.- Based on WWII, correct?
A. Yes it had SP but it was more against bots than any real campaign. B. Correct.
2.- Battlefield 1943... same as 1 or something changed?
Console only, more like Bad Company 1, only WWII based. Used the Frostbite 1.5 engine.
3.- Battlefield:Bad Company... not for PC I gather?
Correct, another console only. First to use the Frostbite engine (1.0).
4.- Battlefield: Bad Company 2... played the campaign, like it, wanted more.
Never finished the SP, then again it is more like BF2 in that MP was the main focus. Also used the Frostbite 1.5 engine.
5.- Battlefield 2 & 2 Special forces... are those MP only, SP, or add-ons to BC2 and are they 2 different games?
There is SP element to them, but again it it only against bots and played on the same maps as MP.
I have also heard of Battlefield Vietnam but know very little of it.
Same as BF1942 only in set in Vietnam, and with Vietnam era weapons and vehicles.
I will not be buying any of the newer games for a while and I rather spend some money on these old games if they were as good as BC2 was... Again, I am only interested in the Campaign.