This has been discussed on the forum before, try a search for the full thread. Short answer is that yes, it is possible IF you match the software versions on export/import first. This is not so much of a problem with the 700/2000/4000 as they will (currently) all run the same versions of code. However, this has not been confirmed to my knowledge by Juniper but I suspect that it is highly unsupported and I would only recommend using for lab/test purposes (or when you really need to :-)
Bear in mind that the 700 is effectily obselete (well, superseded at least) anyway as there is about $500 difference between that at a 10 user SA2500 which has way more features. The other note is that the 700 only has Web, Files and NC and no SAM/TS features; a config from a 2000/4000 with these features can be imported, but obviously they won't work/be enabled. I wouldn't also try and import a 700 config into anything else if I could help it..