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onto the questions at hand...
the pci bus speed spec is 33 mhz, not synchronous with the bus speed of the system (so not 133)...typically there are 'dividers' associated with the fsb of a system to give the pci bus and agp bus their appropriate speeds of 33/66 respectively. For example with a bus speed of 100 mhz, the dividers are 1/3 for the pci clock and 2/3 for the agp clock..or a ratio of 3:2:1 for pci, agp and system respectively.
Now on most NEWER motherboards, there are more dividers to allow the user to change fsb speeds..meaning you can go up to 133 mhz for the FSB but then new dividers kick in and its 1/4 for the pci bus speed and 1/2 for the agp bus speed giving you a ratio of 4:2:1 for pci, agp, system respectively.
First thing to do is find out if your motherboard officially supports a system bus speed of 133 mhz...if it does then it will also have dividers for that speed and your pci and agp bus's will both be running in spec and it wont matter whatever card you use...
if it does not however and you run your system bus at 133 mhz, then your pci clock will be running at 44.33 mhz, not 33 and your agp clock will be running at 88, not 66...dangerously out of spec for both devices, which means youll have to get some damn good quality and expensive devices that would support a higher bus frequency.
regarding the speed of the video card, the bus speed for an 8 or 16mb budget or legacy video card will have no bearing on the performance of the card...you would not ever see any bottleneck issues with anything up to 8mbs...when you start going a little more though, or have a newer graphics card that has a faster gpu and faster memory...then you need a faster bus speed to accomodate that...so between an agp or pci 3d card, the faster option would ALWAYS be the agp card but in some cases it doesnt make a difference because there is no bottleneck with the old 3d pci cards
as far as the graphics card you are going to use...my 2nd computer i bought had an ati rage iic card with 8mb of video memory..it was fine for 2d applications but nothing beyond that..so if you only have the 4mb version dont even think about playing games or doing anything remotely close to photo or video editing...otherwise youll need at least an 8mb card but nowadays 16 is a little more preferrable.
any more questions?
~jeff~