I'm (still) no expert with ISA 2000 - but it sits there happy enough, with pretty much the default installation on our Single Domain topology.
We recently upgraded to a 2meg SDSL line - but the reports I'm getting from online tests report that I'm getting about 1.4meg downstream and 750kbs upstream ... which is pretty short of the 1.5 you would expect up.
I called my ISP who confirmed that I should get approx 1.5 or more in both directions and it's been set up correctly.
I wonder if my ISA Server could be holding back on bandwidth (throttling?) - i've checked the default bandwith rule and it's just set as it was in installation.
Any pointers ?