i just need to get something clear. does the 2000 Outback sport have the same engine as the 2000 RS? some people tell me it does while others say it doesnt so now i'm confused.

yes it does

i thought the outback sport was a 2.2 liter engine, while the forester was the same as the 2.5?

The current engine in the TS, RS, Outback Sport, Forester, Legacy and Outback are all 2.5L flat-four and are all basically the same 165hp engine. The WRX has a 2.0L turbo, the STI and the Forester XT have a 2.5L turbo, and the Outback is available with a 3.0L flat-six.

The 2000 Outback Sport was a 2.2L engine, the 2002 onwards Outback Sport was a 2.5L engine.

Are you sure? I know I've seen some of the old style with 2.5's

I am sure, the spec sheet for the 2000 models shows the Outback Sport as having the 2.2L.

I will PM you the link.

so then, if the obs and rs have the same engine, could someone put parts made for the rs in the obs' engine?

Yes they could, if the particular model years have the same engine but as I mentioned, the 2000 Outback Sport had a 2.2L.

Yes they could, if the particular model years have the same engine but as I mentioned, the 2000 Outback Sport had a 2.2L.
I believe freakray is right. The OBS and L Impreza's came with the 2.2L up to 2001, while the RS had a 2.5L (learn something new every day).