well, you can do that bootdisk/iso thing but a lot of people have posted here saying they can't really do the isos which is why i posted those links to cheap mail order linux distributions.
if you really do want to boot to DOS using a non win9x version of windows, you must boot into windows, put a blank floppy in your drive and then start>settings>control panel, then add/remove programs>emergency startup disk, then follow the dialogue to create a boot disk. reboot with that in the drive and bob's yer uncle, fannie's yer aunt.
now i just tried this in windows 2000 and the bootdisk option is not there in add/remove programs. No doubt it will be somewhere else in control panel, i also attempted to use the 'sys' command to make one, and that's no go as well. maybe you could download the disk image of a DOS bootdisk from bootdisk.com and then use rawrite (or dd if you have installed linux by then) to make a boot floppy.
frankly though, i don't know why you would ever need to boot to DOS once you have linux set up...