InDesign CS6 and Illustrator CS6 are still available and they both run on Windows XP. You can get the CS6 apps either as part of your Creative Cloud membership or as a perpetual license.
The only way you're likely to find versions older than CS6 is on the auction sites, but be VERY careful. Educational licenses cannot be transferred at all, and commercial licenses require the owner to fill out a form and submit it to Adobe, and they cannot transfer any version that was used as part of an upgrade chain without transferring every version in that chain.
CS6 should still work on XP, and should be available direct from Adobe, but you'll probably have to work to find it on the site.
Thanks: Mark, Peter:
I've found InDesign & AI on the Adobe site. If I qualify as a student, I can join for $19.99/mo. & have access. (which I can afford. I AM a student, but I'm not certain how I'd "officially" qualify as one . . .
You'd need to have proof that you are enrolled in an accredited secondary school. I think you'll find the requirements if you search the site for education licensing, and probably if yu try to signe up for it, too.