Yeah, that machine doesn't appear to have either PCIe (PCI Express) or AGP slots.
While the game probably won't suffer from extra video memory, PCI's really not an optimal way to connect a video card (if it were, there wouldn't be AGP at all).
64MB video cards are pretty affordable. I'd suggest using one of those instead. The 128MB card wouldn't hurt, but at the end of the day you'd still have a low-end computer that's not built for gaming, and the investment isn't something you're going to be able to carry over into another machine very well.
Also, make sure the fact that it's a PCI card rather than AGP won't cause a problem for the games you have in mind. It sometimes does.