I can tell you from personal experience that XP has no problems whatsoever with reading/writing floppy disks if your floppy drive is good. I have an ancient Compaq Presario 7360, manufactured in 2000. It has a 500MHz AMD K6-2, 512MB of RAM, a 120GB IDE HDD, a CD-RW drive, and a floppy drive. The floppy drive is bog standard, the same one the system came with, and 18 years later it still works fine under Windows XP (I've also run 98SE on it, which is what it was designed to run, but XP makes it possible to use more software). I'd still be running that K6-2 on a daily basis if it wasn't for the weak USB 1.1 ports that don't always work when you boot the system up (I've thought about getting a USB 2.0 card, but it seems excessive for a K6-2, and better suited for a Pentium III).
My DC5000 SFF also has a floppy drive, though unfortunately it has died. If I'm not mistaken the final systems released with floppy drives integrated, and/or motherboards that have a built-in option for installing a floppy drive (i.e., without the need arising of having to connect a USB floppy drive), came out during the Core 2 Duo era (and to a lesser degree first-generation i3/i5/i7 systems).