crunching into reverse is a really common
problem with alot of cars, it's basicly because theres no syncromesh on the reverse gear.
as some people have said put it in 1st then into reverse, also ensure you are fully depressing the clutch pedal, and you'll be fine, aslong as it doesn't crunch into any forward gears.
As for the gear oil change, do it anyway, it shouldn't be expensive, and it can only be a good thing surely? i know i'll be doing mine when the better weather comes.
If it's a hydraulic clutch (not sure what the 1.4 has) it might also be worth bleeding the slave cylinder?