Look in the boot by the spare wheel there is a label with the engine code, get me that.
If its 5 speed it will likely be 110bhp and 6 speed 115bhp, i believe those to be the figures on the pre 2001 engines.
I would assume they all remap well.
If you want something fast, cheap and diesel then consider a Vectra C, i have a Face Lift base model, you need one with the Z19DTH engine, which produces 150BHP and a sh*t load of Torque, you can map them to 185BHP and buy them for peanuts.
The Sportier looking Astra 3 or 5 Doors with the same engine sell for double the cost or more and your not saving an awful lot of weight.