Hi all!
I started having this problem some 3 weeks ago on my G5, 2.5 bi-pro running Tiger 10.4.8. Most of my downloads whether using Firefox 1.5 or 2.0, Safari, or a download manager (iGetter, DownThemAll...) would end up being corrupted. The file size would match up, but the MD5 when available would not. On installing or drag-and-dropping, a -36 error would pop up or an error indicating a read or write problem on some component. I repaired permissions, ran DiskUtility, AppleJack... to no avail. Other user sessions (root or otherwise) would yield no better result. I am stumped and would greatly appreciate any help out there.