[Blarg]

The 4700 and 4600 are machines with PCI slots and an AGP slot for the video card.

The market in both motherboards and video cards is changing to PCI Express(like in the 8400) and dropping the AGP slot. If you want to upgrade down the line, particularly video cards, it will be much easier in a machine like the 8400 that has PCI Express slots.

You may still be able to get AGP cards for quite a while, but you won't need to upgrade for quite a while, either. And you can get a perfectly good AGP-based video card now that will last you for years unless you really intend to stress your system with the latest and greatest games -- and even those play pretty well on the better AGP cards out today, like the ATI 9800's. At any rate, by the time you decide to upgrade your video card(usually the most necessary reason to upgrade a home system), AGP cards may not be around as widely, and it may be harder to do. Furthermore, they probably will not be much better than the cards you are going to buy today.

Worse, though, is the matter of drivers. It's very common for manufacturers to do a pretty miserable job on upgrading their drivers, whether it's for new operating systems, new versions of DirectX, whatever. Even stuff that's brand new on the shelves can have drivers that are many months old. This is reciprocated by Microsoft's often not recognizing and working properly with old drivers and hardware when they do upgrades of DirectX or various aspects of their operating systems. New operating systems are expected out from Microsoft in the next year or two, also. On both sides of the "Who is going to support my hardware?" question, it adds up to trouble and shifting the blame, or just painfully slow updates that make your equipment work properly. I doubt manufacturers will put much effort into working on adapting their drivers to models of video cards they no longer make or make in quantity.

So on the software and hardware side, there are strong reasons to stay away from AGP systems and get into PCI Express systems instead. The latter systems as a whole are not really notably faster yet, unfortunately, so what you're buying is mostly future proofing.

The argument for staying with AGP is that those systems are often cheaper, occasionally much cheaper. Another argument is that by the time you outgrow what you've got, you'll just buy new again instead of upgrading, and the couple or few hundred dollars you save now are not illusory savings at all when you have no intention of ever upgrading anyway.

That's probably not the most cost-efficient way to go about things, but to each their own; there's plenty of merit to that argument if upgrading components one by one is not your thing or if you have money to burn and just buy new systems instead.