add remote/frontrow to g4 mac mini?

Your signature line indicates you are running MacOS 10.5.1, which includes a fully functional installation of Front Row (red armchair icon in the Applications folder), so the software is already present and usable. Of course the G4 minis didn't have an IR port, so the remote supplied with all new Macs won't work with it, but there are a few alternatives that can be used.

Just trying to locate the most commonly suggested one....... http://www.salling.com/Clicker/mac/ added to a suitable cellphone or handheld device for example or the Keyspan remote at http://www.keyspan.com/products/errf1/

it's Tiger on the mac mini.

Ah, well then you may be out of luck! There have been hacks published to get the earlier copies of Front Row to work under Tiger (and working quite well it should be said), but they aren't supported by Apple, so they can't really be discussed here. A google search might help however!

Sadly there is no way to add the IR port present on Intel systems to a G4 mini, and thus use the Apple remote. Is there a reason you are only prepared to accept that option rather than perhaps the keyspan device instead?

No, it's not an available part or upgrade, and would not have anywhere to interface to on a G4 mini.

If you were planning to put the mini to use as a media center system and it has no other primary function, the cost of adding leopard and a keyspan remote is not that great for a solution that is actually pretty sophisticated and certainly very functional. I have a 1.5 mini in use doing this (though controlled with cordless keyboard) and which gives me access through Front Row to my entire DVD collection, along with my iTunes library etc. I've found it well worthwhile.