The DVD decoder card won't work in anything lower than a G3 (trust me, I've tried).
I should parenthetically mention: some people love Radeon PCI cards in their system. These are decent cards and on paper will be faster than the Rage 128, but they have three issues: 1) Radeon gets starved for data over the PCI bus as opposed to AGP more than the earlier Rage chipsets did, negating a lot of their performance improvements 2) they can be quite a bit more expensive, since they are less common and 3) they have weird compatibility glitches with some games, such as bad polygon models in Shogo and Quake II, and not all of the affected titles have patches available. If you can get one cheap and know that your software will work, it's a good option, but the R128 cards are not that much slower in practice, more compatible and more easily available for less cash.
I should parenthetically mention: some people love Radeon PCI cards in their system. These are decent cards and on paper will be faster than the Rage 128, but they have three issues: 1) Radeon gets starved for data over the PCI bus as opposed to AGP more than the earlier Rage chipsets did, negating a lot of their performance improvements 2) they can be quite a bit more expensive, since they are less common and 3) they have weird compatibility glitches with some games, such as bad polygon models in Shogo and Quake II, and not all of the affected titles have patches available. If you can get one cheap and know that your software will work, it's a good option, but the R128 cards are not that much slower in practice, more compatible and more easily available for less cash.