I went from an EOS 500N (purchased 1996 – ish) to a new 300D in 2003 and took with me the 28-80mm standard Canon lens and a Canon 75-300mm USM 2 lens (same pair of lenses as you have, i guess)

They both work just fine with the 300D – search my other posts for example images. F-stops and autofocus work exactly the same as the 500 and you will find the control layout very similar on the camera body.

I would recommend buying the 350D ( or secondhand 300D ) kit with 18-55mm lens as it is a half decent wideangle zoom for the extra £70 ?? or so and is not available as a separate lens to purchase.