You can access internet with any ISP in OsX. But features like iDisk might require Apple's service like .mac - because iDisk stores files on Apple's server so that you can access them online. When you take a .mac account, you will get 250 MB of combined iDisk and .mac mail storage. Hope it is clear
There a couple of internet access issues that might come up, mostly in using OSX at home:
* an ISP might not be Mac savvy, and be unable give help if you had any problems setting up your connection.
* the ISP might provide you with a DSL modem, router, etc. with a Windows-only configuration program.
I think both of these are less of an issue than they used to be. In any case, if I was giving advice to a non-techie about get a high-speed internet connection for their Mac, I'd say to find a Mac-friendly ISP. Usually this isn't hard to do.