If you haven't been picking these up as they're announced, Amazon decided to finally give you a way to get all 25 with one click over at their 25 Days of Free page (amazon.com) - scroll down past the days to find the checkable list and "Buy selected song" button.
Oh, one more thing - if you're GIFTING MP3s, Amazon says that you can get $2 off with the code GIVEMP3S. Details about THAT over here.
I encounter major instalation problems with ITunes for Win 2000, had to reboot with Last Good Profile after 2 hours of trying to get safe mode to work... I deleted and reinstalled it, still with problems but now at least it's working.