Here's a full list of models by year.
Up to MY2000, lowest to highest.
I (petrol) or Di (diesel)
Xi (petrol) or Di (diesel)
XEi (petrol) or DXi (diesel).
There were a few different models thrown in for various events, like the 50th anniversary FL1 (1998), which were generally based on higher specs, often with options added.
After the MY2001 redesign, the models changed designation, and later on in the production run, some special models came out with names of way points on the Camel Trophy Run I think.
The i and Di became the "S", also Maasai.
The Xi and Di became "GS" also Serengeti.
The XEi and DXi became the ES and Kalahari.
After MY2003, the ES Premium came out, with a better audio system from Harmon Kardon.
After the Facelift came out, the model designation changed again following the same theme as before, and being similarly equipped too.
"E" Being the basic model, only available in 1.8K and TD4 manual. Equivalent to previous i and S models (just to confuse).
"S" Again only available in 1.8K TD4 manual, equivalent to GS models.
"SE" was equivalent to the ES, but without the sunroof.
HSE was the equivalent of the ES Premium.
The Sport came out after Facelift.
Sport, similar to the SE.
Sport Premium, similar to the HSE.
I think I'm reasonably accurate, as this was from memory.
Hope this helps.