are my canon eos 300 lenses compatible with eos rebel txi?

Answer 1

Yep. You can use them on any Canon digital SLR, including the Rebel XTi.
Just take into account that the Rebel XTi magnifies your lenses by a factor 1.6. This is because the XTi's sensor is smaller than a frame of film. This magnification is great news for your tele-lenses - more reach for free - but it's a bit of a nuisance with standard zooms and wide angle lenses.
The kit lens for the XTi is a cheap Canon 18-55mm zoom (effectively 29-83mm). You could consider getting this to regain wide angle coverage. Or if you're willing to spend, the $500 Canon 17-85mm makes a great standard zoom.

Answer 2

sure