I'm not sure on the 2000 model RX's however the earlier RX's had different g/box & clutch set up to the WRX of a similar year. RX used a cable push clutch and trans without dip stick as opposed to the WRX with hydraulic pull clutch and gearbox with dip stick. If the same set up was used on the 2000 RX, you'd need a complete WRX front cut (inc g/box) and have to install all the mechanicals, complete front loom/
ecu, g/box and clutch hydraulics (master & slave cylinder, lines etc) and possibly the pedal box. I'd also at least inspect the clutch & flywheel which may be cactus, replace the fuel pump and have the injectors from the front cut engine cleaned too.
The job is bolt on, however time consuming and like any conversion there are a few tricks.
Easiest way (as Teejay & Pimpreza have already said) is to sell RX and buy WRX.