Hello & a warm welcome!
iDisk is no longer supported by Apple.
I assume you had a .mac/MobileMe account at one time?
If so, go to System Preferences>.Mac or MobileMe and remove your username and password.
Unmount any iDisk you may have.
If it should fail to dismount then, (Yeah crazy deal), either reboot, or open Terminal & paste in this exact line...
sudo umount -f iDisk/
It'll ask you for an Admin password that won't be echoed, but hit enter/return anyway.
Snow Leopard/10.6.x Requirements...
* Mac computer with an Intel processor
* 1GB of memory (I say 4GB at least, more if you can afford it)
* 5GB of available disk space (I say 30GB at least)
* DVD drive for installation
* Some features require a compatible Internet service provider; fees may apply.
* Some features require Apple’s MobileMe service; fees and terms apply.
Which apps work with Mac OS X 10.6?...
Buy Snow Leopard > http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard
Call Apple Sales...in the US: 1-800-MY-APPLE. Or Support... 1-800-275-2273