Just got new PC, and needed to know before I bought a new card: can I put an 8x card in a 4x slot? I was looking into getting the 9600Pro but can only find it in 8x (would it be totally useless getting it over a 4x card since it’s a 4x slot?) Also, the PC came with a pair of wires going into the speaker output and microphone input in the back. The wires were coming from the inside of the PC through a hole through the metal PCI slot covers. I opened the side of the case and the wires run through into the front near the power button area, then kind of dissapear through plastic so I can’t see where they end up. Any idea what the hell the deal is there (I plan on running a headphone output on there to my reciever)…
Newer AGP cards and slots are no problem. I’ve encountered some problems with old 1x and 2x incompatibilities having to do with voltage levels but I’ve never heard of any problems with anything released in the last 3-4 years. I wouldn’t get too hung up about AGP bus speeds. Unless the rest of your hardware is absolutely top shelf, bottlenecks in CPU and system RAM performance are more likely. If you don’t do any 3D gaming, even a PCI card is more than fast enough.
An 8x should work just fine in a 4x slot. And there isn’t much of a speed difference - few games even max out a 4x AGP speed.
The 9600 Pro supports 4x and 8x AGP. If you’re going to be gaming the 9600XT is a better choice but it costs a little more.
There should be a door on the front of the box that has the headphone jack behind it, keep looking. 
I’ll agree with everyone else and take it a step further. 8x AGP is a scam and has never been properly implemented. A lot of people on ATI message boards have posted that switching from 8x to 4x solved re-occuring system crashes.
I have my ATI 9700 Pro set to 4x, even though I have an 8x motherboard.