Nigel,
Mahler 7 is a particularly difficult work and not to be recommended for someone starting out with Mahler. To make matters worse, this was not a particularly impressive performance (or, at least, when I attended their concert in Edinburgh on Thursday it wasn't particularly impressive). If you haven't already tried, the best starting point is the first symphony.
Mariss Jansons has just made a fine recording on the Concertgebouw's own label (his
previous effort with the Oslo Philharmonic is even finer but comes coupled with a slightly less good 9th, which is probably not a good introduction and is therefore a little pricier),
Mackerras has a cheap recording with the RLPO on classics for pleasure and the
Bernstein recording with the Concertgebouw is also very fine (though this is only available coupled with his recording of the 5th which, while remarkable, is not a good starting point).
Nick, I miss the days of proper simulcasting.....
regards, Tam