Cnr Dinh Liet and Hang Bac, Hoan Kiem dist., on Hang Bac on the NE side - expensive but excellent quality internet cafe - there's a sign out the front, head straight through the sort of indoor laneway to the back and up one flight of stairs - it's easier to find than it sounds - good CD facilities.
If you just want a CD copied though, try just about any shop that sells software, computer things or even a camera joint who burn photos, they might be able to help...
