YES YES! A big YES. It will work lik a charm Ive done stuff/testing in the past and can say its 100 percent it will work.
You will not see a performance decrease BTW booting with 4x AGP compared to 8x AGP. So don't worry about that your getting pretty much same performance either way.
That AGP 4x must be a old card, You can even upgrade to a AGP 1950XT or 7800 GS agp.
good luck let us know what your going to buy thanks,, gl