Total texture memory: 3dMark2000 trouble

There´s a test in mad onion´s 3dMark2000 Benchmark that´s called Texture rendering Test. One version of that test (called´64MB´) refuses to run on a Rage Fury pro (128pro), a Fujitsu Prolink (tnt2m64), a Matrox Millenium (G200) and a Diamond Stealth III (Savage4). None of these cards can access sufficient system memory, though AGP aperture is set to 256 MB. The only card I could get my hands on that ran the test was an Elsa Gloria III(GeForce2). As far as I know, I used the latest driver version for each card. Now, what the hell limits the amount of memory that can be accessed via the AGP?