Where's the oil filter on a 1999 astra 1.8 16v eco tech engine?

EH!!! Whoever told you that wants hitting. There are 2 types of 1.8 engines, the older X18XE1 engine and the newer Z18XE, the old type uses a replacable element I believe whilst the newer Z18XE uses the more common cannister type. By the age of yours you've definetely got the X18XE1 engine, the Z18XE didn't come out till 2000, go into any Vx dealer and ask for an oil filter for that engine, the filter is located right at the front of the engine, look down behind the radiator and you should see it.

Ken
October 2006