You can use iPod with a PC, I do it every day. The software is rather buggy right now, but it does work. I sure as hell wouldn't buy a Macintosh just for iPod use.
As far as comparable products ... any of the plethora of HD-based portable players will work. The problem is, they are larger and uglier than iPod (by far). iPod also has much better battery life, and, not to be missed ... Firewire (1394) transfers. Significantly speedier than USB.