You might try Goliath (SP?). It is a program designed to allow you to access web folders which are common on the PC side. It uses a different protocol than a standard mount of the iDisk.
I was happy to find out I could set it up using a web folder interface because it allowed me to create a web folder for it on my computer at work. It makes a good replacement for a floppy, I can upload one place and download at the other...
All and all though, I think iDisk is relatively fast. I remember at one point downloading an update to a program that the company housed on an iDisk as a mirror. The transfer rates I got were the fastest I've ever gotten though the connection, over 100k per second...