Did you downloaded the related DCU file? On the same page, 5 lines under the ibo4.zip link you have:

DCU Packs
...
Delphi 3 DCU's to use with eval kit above. D3_DCU.zip (360 KB)

You would better download and install Firebird final 1.0 too.

Hope this will help
Regards
Marco Menardi
btw, 3 days ago I was in panic for a similar problem, trying to help a fiend of mine, and thinking there was a lot missing from the evaluation Ibo kit ;)

--- In IBObjects@y..., Duilio Foschi <dedalus@y...> wrote:
> --- In IBObjects@y..., "Jason Wharton" <jwharton@i...> wrote:
> Your code is out of date. Please get the latest
>
>
> I downloaded ibo4.zip from www.ibojects.com
>
> I can find no *.dpl file.
>
> How am I supposed to install the new code in Delphi 3 ?
>
> Thank you
>
> Duilio Foschi