easiest swap is a 1.4 16v as thats a standard polo engine, comes with 100BHP as standard.
Then add a ported and polished head with larger exhaust valves, fast road cams, 4-2-1 manifold, full decat stainless system,lightened and balanced flywheel k&n panel filter in smoothed OE box, pair twin 40 carbs and the relevant ignition management and your looking 150bhp minimum, in a small light car like a polo thats more than enough believe me. A grand all in and you'll have a rather large smile on your face. then budget another £1k to seriously sort the handling/brakes. it will be nippy enough to see most things off the line, and will outcorner most cars too.
The amount of money you'd be looking at spending for a 450bhp 4wd polo is well in excess of £10K... seriously not worth it. you could buy an R32 for that money