Ich glaube, die beiden sind synonym (vielleicht Unterschied im Sprachniveau?)
Hab mal bei reference.com nachgeschaut und da steht für "further":
–adverb 1. at or to a greater distance; farther: I'm too tired to go further.
2. at or to a more advanced point; to a greater extent: Let's not discuss it further.
3. in addition; moreover: Further, he should be here any minute.
–adjective 4. more distant or remote; farther: The map shows it to be further than I thought.
5. more extended: Does this mean a further delay?
6. additional; more: Further meetings seem pointless.
http://dictionary.reference.com/browse/further